Stripy chocolate, vanilla and coffee cake

At Sharp Labs we're having a baking competition going on to raise money for Helen & Douglas House. I foolishly decided to enter it.

There are three rounds. The first round, which took place on the 25th November, was sponge cakes. I invented a variation on a coffee cake. It's made up of six alternating layers of chocolate and vanilla sponge, bound together and coated with a coffee buttercream icing. This recipe is for a large cake which will happily make 16 slices.

Ingredients

For the vanilla sponge:

• 165 g unsalted butter (at room temperature)
• 165 g caster sugar
• 3 large eggs
• 165 g self raising flour, sifted
• 1.5 tsp vanilla essence
• Hot water (if required)

For the chocolate sponge:

• 165 g unsalted butter (at room temperature)
• 165 g caster sugar
• 3 large eggs
• 155 g self raising flour, sifted
• 1 heaped tbsp cocoa powder, sifted
• Hot water (if required)

For the coffee buttercream:

• 600 g icing sugar
• 375 g unsalted butter (at room temperature)
• 150 ml strong espresso coffee (about 3 shots)

Method

Preheat the oven to 155 ℃ (fan). Position a shelf near the middle of the oven for the cakes. Line the bottoms of two deep 20 cm springform or sandwich tins with baking parchment.

Each of the sponge batters is prepared in the same way (it's best to do prepare them in parallel in two bowls so that you can bake the cakes simultaneously):

1. Cream butter and sugar together using an electric hand mixer until light and fluffy.
2. In a measuring jug, beat the eggs. Then add them little by little to the butter & sugar mixture, making sure to fully combine each addition before the next. For the vanilla sponge, add the vanilla essence at this stage.
3. Sift about a quarter of the flour (or flour and cocoa mixture) into the mixture, from a height of about 50 cm so as to air the flour well. Carefully and gently fold the flour in (you want to trap as much air as possible at this stage). Repeat until all the flour has been combined.

Transfer the sponge batters into the tins, and place the tins at mid-level of the oven near the front. Bake for 25-30 mins. When they are cooked, they'll (1) make a popping sound like rice crispies, (2) feel springy when lightly touched near the centre with a fingertip and (3) a sharp knife inserted all the way through will come out clean.

About 1-2 mins after removing the cakes from the oven, turn them out, carefully peel off the baking parchment, and leave them to cool for about half an hour.

Carefully slice each of the cakes into three horizontal slices, approximately 1 cm in thickness. I found that a very very sharp knife and a lot of patience was more successful than using a cake wire.

Make the buttercream by putting the butter and icing sugar into a bowl and beating them with an electric hand mixer while slowly adding the espresso.

Assemble the cake by putting a vanilla slice of sponge on a turntable, adding a thin layer of butter cream and levelling it off, then adding a chocolate slice on top, and continuing until all six slices are built up. Make sure on each layer to spread the buttercream all the way to the edge.

Use the remaining buttercream icing to smoothly coat the exterior of the cake. Use a side scraper and a turntable to get vertical sides and horizontal top! You should have some icing leftover.

Finally, you can optionally use cocoa powder and/or walnuts to decorate the finished cake.