Chocolate Fudge Cake with custard is £5 on our menu and it is the dessert people order without reading the rest of the list. A rich, moist chocolate sponge, layered and topped with a smooth fudge frosting, served with warm custard poured over the top. This is the home version, and it makes a cake that serves twelve.
The sponge is an oil-based one rather than a butter-and-sugar creamed sponge, made with boiling water and cocoa. That sounds like a strange method and it is the reason the cake stays properly moist for days. Oil does not set solid in the fridge the way butter does, and blooming the cocoa in boiling water deepens the chocolate flavour considerably.
The frosting is a proper fudge frosting made with melted dark chocolate, butter and icing sugar, not a buttercream. It sets to something dense and slightly chewy at the edges. And the custard is the part not to skip — warm custard against cold fudge frosting is the whole point.
Why this recipe works
- Cocoa bloomed in boiling water. Hot liquid dissolves the cocoa solids properly and releases far more flavour than mixing cocoa into a dry batter. It also makes the batter very loose, which is normal and correct.
- Oil instead of butter in the sponge. Oil stays liquid at fridge temperature, so the cake is still soft on day three. Butter sponges firm up and taste dry within a day.
- Buttermilk and bicarbonate of soda. The acid in the buttermilk reacts with the bicarb to give a fine, even crumb, and it adds a slight tang that stops the cake tasting flatly sweet.
- Dark chocolate in the frosting, not just cocoa. Melted chocolate brings cocoa butter, which is what gives the frosting that dense fudge set rather than a grainy icing-sugar texture.
- A pinch of salt and a spoonful of coffee. Neither makes the cake taste salty or of coffee. Both make it taste more of chocolate.
- Warm custard served separately. Poured at the table so the frosting does not melt into it before it reaches you.
Ingredient notes
Cocoa powder. Use a good unsweetened cocoa, not drinking chocolate, which is mostly sugar and milk powder. Dutch-processed cocoa gives a darker colour and a smoother flavour if you can find it.
Dark chocolate. Around 60 to 70 per cent cocoa solids for the frosting. Higher than 70 and the frosting turns slightly bitter and sets very hard. Ordinary supermarket dark chocolate is completely fine here — this is not the place for anything expensive.
Buttermilk. Small cartons in the dairy aisle. If you cannot find it, stir a tablespoon of lemon juice into 250ml of whole milk and leave it ten minutes until it thickens slightly.
Sunflower oil. Neutral flavour. Vegetable or light rapeseed oil work equally well. Do not use olive oil, which is too strongly flavoured for this.
Instant coffee granules. One teaspoon dissolved in the boiling water. You will not taste coffee, you will taste a deeper chocolate. Leave it out if you are baking for children and it will still be very good.
Custard. Ready-made fresh custard from the chilled aisle is what most people will use and there is nothing wrong with it. A proper crème anglaise takes fifteen minutes and there is a version in the recipe notes.
Substitutions and variations
Traybake instead of a layer cake. Bake the whole batter in a lined 20 x 30cm tin for 35 to 40 minutes, then spread the frosting straight over the top. Easier to portion and easier to transport.
Cupcakes. Makes about 20. Bake at 170°C fan for 18 to 20 minutes and pipe the frosting on once completely cool.
Add a fudge layer. A thin layer of dulce de leche or caramel spread under the frosting in the middle turns this into something much closer to the Chocolate Dream Cake Tin on our menu.
Dairy free. Use a plant-based milk soured with lemon juice instead of buttermilk, dairy-free dark chocolate and a hard baking margarine in the frosting. We have not tested this version, so treat it as a starting point and check every label yourself.
Serve it warm. Twenty seconds in the microwave per slice, then the custard over the top. The frosting goes molten and it is a completely different pudding.
Skip the custard. Cream, vanilla ice cream or crème fraîche all work. Crème fraîche is the interesting one, because the sourness cuts the sweetness.
Step-by-step guidance
The full method is in the recipe card below. Four things are worth getting right.
The batter will be very thin. Once the boiling water goes in it will look more like a thick hot chocolate than a cake batter. This is correct. Do not add extra flour to thicken it — that thin batter is what produces the moist crumb.
Lining the tins. Grease and line the bases with baking paper, and grease the sides. This batter is wet and sticky, and a cake that welds itself to the tin is a genuinely upsetting way to end an hour of work.
Knowing when it is done. Thirty to thirty-five minutes at 170°C fan. The top should spring back when pressed lightly and a skewer should come out with a few moist crumbs on it, not wet batter and not completely clean. Completely clean means you have gone slightly too far.
The frosting. Melt the chocolate and butter together gently, either over a pan of barely simmering water or in short bursts in the microwave, stirring between each. Let it cool for five minutes, then beat in the sifted icing sugar and cocoa with the milk. Sift the icing sugar — it takes thirty seconds and it is the difference between silky and gritty. If the frosting is too stiff, add milk half a teaspoon at a time. If it is too loose, let it sit for ten minutes and it will firm up as the chocolate cools.
Professional tips
- Weigh everything. Baking is not cooking, and cocoa and flour in particular go badly wrong measured by volume.
- Have the eggs and buttermilk at room temperature. Cold ingredients make the batter seize slightly and bake unevenly.
- Level the sponges with a bread knife before frosting if they have domed. A flat cake is a stable cake.
- Cool the sponges completely — genuinely cold, not just warm. Frosting on a warm cake slides straight off.
- Use a palette knife dipped in hot water and wiped dry to smooth the frosting. It glides instead of dragging.
- Warm the custard gently and do not let it boil, or it will split. Just below a simmer, stirring.
Troubleshooting
| Problem | Likely cause | Solution | Prevention |
|---|---|---|---|
| Cake is dry | Over-baked, or extra flour was added to the thin batter | Serve warm with plenty of custard | Trust the thin batter and check at 30 minutes |
| Cake sank in the middle | Oven door opened too early, or under-baked | Cut out the centre and serve as squares | Do not open the oven for the first 25 minutes |
| Frosting is grainy | Icing sugar was not sifted | Beat in a tablespoon of warm milk and keep beating | Always sift the icing sugar and cocoa |
| Frosting is too runny to spread | Still warm from the melted chocolate | Leave it 10 to 15 minutes at room temperature | Cool the melted chocolate for five minutes before adding the sugar |
| Frosting set rock hard | Chocolate above 70 per cent, or too much icing sugar | Beat in warm milk half a teaspoon at a time | Use 60 to 70 per cent chocolate and weigh the sugar |
| Cake stuck to the tin | Tin not lined and greased | Warm the base of the tin gently and run a knife round the edge | Grease and line the base, grease the sides |
| Custard split or went lumpy | Boiled | Blitz it briefly with a stick blender | Warm it gently, stirring, and never let it boil |
What to serve with it
Warm custard is the house answer and the reason it is on the menu that way. Vanilla ice cream, pouring cream or crème fraîche are all good alternatives, and a few raspberries on the side cut the richness surprisingly well.
If you are putting a whole meal together, this follows almost anything from our menu. It is particularly good after something spicy — chilli oil beef ramen or Demon wings both leave you wanting exactly this. More sweet things in our dessert recipes.
Storage and reheating
This cake keeps better than most, which is the advantage of an oil-based sponge.
Store it in an airtight container at cool room temperature for up to three days. Do not refrigerate it unless your kitchen is very warm — the fridge dries cake out and firms the frosting to the point where it loses its fudge texture. If you do refrigerate it, bring slices back to room temperature for 30 minutes before serving.
To serve warm, microwave a slice for 20 to 25 seconds. The frosting goes molten and the sponge softens.
Freezing: the unfrosted sponges freeze very well for up to three months. Cool completely, wrap tightly in cling film and then foil. Defrost at room temperature for three hours before frosting. Frosted slices can also be frozen individually for up to a month, though the frosting surface will dull slightly.
Custard should be reheated gently in a pan and never boiled. Do not reheat custard more than once.
Frequently asked questions
Why is the batter so runny?
Because of the boiling water. It is meant to be. A thin batter is what gives you a moist, tender crumb, and every well-known chocolate fudge cake recipe works this way.
Can I make it a day ahead?
Yes, and it is arguably better on day two once the frosting has settled into the sponge. Keep it in an airtight container at room temperature.
Can I use a different tin size?
Two 20cm round tins is the recipe. Two 18cm tins will need about five minutes longer and give a taller cake. A 20 x 30cm traybake tin needs 35 to 40 minutes. Adjust and check with a skewer rather than trusting the clock.
Do I have to use buttermilk?
No. Stir a tablespoon of lemon juice into 250ml of whole milk and leave it for ten minutes. The result is very close.
Is the coffee noticeable?
No. One teaspoon in a cake this size is a background flavour enhancer, not a coffee flavour. Leave it out if you would rather.
Can I make the frosting in advance?
Yes, up to two days. Keep it covered at room temperature, not in the fridge, and beat it briefly before using. If it has stiffened, beat in a little warm milk.
Is homemade custard worth it?
If you have fifteen minutes, yes — the difference is real. There is a method in the recipe notes. On a weeknight, good fresh custard from a carton is a perfectly respectable answer.
PrintChocolate Fudge Cake with Warm Custard
- Total Time2 hours
- Yield12 slices 1x
A deeply moist oil-based chocolate sponge with cocoa bloomed in boiling water, layered and topped with a dense dark chocolate fudge frosting and served with warm custard.
Ingredients
For the chocolate sponge
- 250g plain flour
- 350g caster sugar
- 75g unsweetened cocoa powder
- 1.5 tsp bicarbonate of soda
- 1 tsp baking powder
- 1/2 tsp fine salt
- 2 large eggs, at room temperature
- 250ml buttermilk, at room temperature
- 125ml sunflower oil
- 2 tsp vanilla extract
- 250ml boiling water
- 1 tsp instant coffee granules
For the fudge frosting
- 200g dark chocolate, 60 to 70 per cent, broken up
- 150g salted butter
- 250g icing sugar, sifted
- 30g unsweetened cocoa powder, sifted
- 3 tbsp whole milk
- 1 tsp vanilla extract
To serve
- 600ml fresh custard, warmed
Instructions
Bake the sponges
- Heat the oven to 170°C fan. Grease two 20cm round cake tins, line the bases with baking paper and grease the sides.
- Whisk the flour, caster sugar, cocoa, bicarbonate of soda, baking powder and salt together in a large bowl.
- In a jug, whisk the eggs, buttermilk, oil and vanilla together. Pour into the dry ingredients and mix until just combined.
- Dissolve the coffee granules in the boiling water, then pour it into the batter and mix until smooth. The batter will be very thin, closer to hot chocolate than cake batter. This is correct — do not add more flour.
- Divide between the tins and bake for 30 to 35 minutes, until the tops spring back when pressed lightly and a skewer comes out with a few moist crumbs on it. Do not open the oven for the first 25 minutes.
- Cool in the tins for 10 minutes, then turn out onto a wire rack and cool completely. They must be genuinely cold before frosting.
Make the fudge frosting
- Melt the chocolate and butter together gently, either in a bowl over barely simmering water or in the microwave in 20 second bursts, stirring between each. Leave to cool for 5 minutes.
- Beat in the sifted icing sugar and cocoa with the milk and vanilla until smooth and glossy. If it is too stiff, add milk half a teaspoon at a time. If it is too loose, leave it 10 to 15 minutes to firm up as the chocolate cools.
Assemble and serve
- Level the sponges with a bread knife if they have domed. Sandwich them with a third of the frosting, then spread the rest over the top and sides, smoothing with a palette knife dipped in hot water and wiped dry.
- Warm the custard gently in a pan, stirring, until hot but not boiling.
- Cut into 12 slices and pour the warm custard over at the table.
Notes
The batter is meant to be thin. Once the boiling water goes in it will look far too runny. That thin batter is exactly what produces the moist crumb. Do not add extra flour.
Make your own custard if you have 15 minutes. Whisk 4 egg yolks with 50g caster sugar and 2 tsp cornflour. Heat 500ml whole milk with 100ml double cream and a split vanilla pod until steaming, pour it slowly onto the yolks whisking constantly, return to the pan and stir over a low heat until it coats the back of a spoon. Never let it boil.
The coffee is not a coffee flavour. One teaspoon in a cake this size simply makes the chocolate taste deeper. Leave it out if you are baking for children.
Traybake version. Bake the whole batter in a lined 20 x 30cm tin for 35 to 40 minutes, then spread the frosting straight over the top.
Serve it warm. Twenty to twenty-five seconds in the microwave per slice makes the frosting molten. With warm custard over the top it becomes a completely different pudding.
Storage. Airtight container at cool room temperature for up to 3 days. Refrigerating dries the cake and hardens the frosting. Unfrosted sponges freeze well for up to 3 months, wrapped in cling film then foil.
Equipment. Two 20cm round cake tins, baking paper, a large mixing bowl, a balloon whisk, a sieve for the icing sugar and cocoa, a wire cooling rack, a bread knife for levelling and a palette knife for the frosting.
Allergens. This recipe contains wheat (gluten), milk, egg and soya (most dark chocolate contains soya lecithin). Some cocoa powders and chocolates carry nut and peanut cross-contamination warnings. Always check the label of every ingredient you use, as recipes and allergen information can change. People with food allergies or intolerances must also consider cross-contamination.
This is a home recipe inspired by the Chocolate Fudge Cake with custard at The Cozy Bowl. It is not the restaurant’s exact commercial recipe.
Or have a slice while you are with us
An hour of baking for one slice of cake is not always the right call. Chocolate Fudge Cake with custard is £5 on our menu at 172 Biscot Road in Luton, and the Chocolate Dream Cake Tin next to it is £6.50 if you want layers of mousse and ganache instead. Order for collection or delivery, or read the full dessert list.
If you bake it at home, rate the recipe below and tell us whether you managed to wait for it to cool.
Newer From Our Kitchen
If you would rather not turn the oven on, our chocolate dream cake tin is a no-bake mousse and ganache cake with a chocolate shell to crack through. Either one is very good with a karak chai alongside.