There is inevitably a little bit of wastage with this recipe, but any leftover cakes can be kept in the freezer until you’re ready to make another work of art. Avoid eggs with deep-orange yolks – you want your white sponge to be as pale as possible. A battenberg tin is ideal, but you can also use three small loaf tins (as shown below), or cook the cakes in batches. The sour cream helps create a sturdy cake.
You will need
1 x 20cm square tin
3 x 450g loaf tin (measuring approx 16cm x 11cm x 7cm) or 1 battenberg tin
For the cakes
500g unsalted butter
500g caster sugar
500g sour cream or Greek yoghurt
750g self-raising flour
1 tsp of salt
Red, blue and yellow food colouring gels or paste
For the ganache
400g dark 50% chocolate, chopped
300ml double cream
1. Preheat the oven to 180C/350F/gas mark 4. Grease and line the base and sides of your tins with baking paper.
2. In a large bowl, cream together the butter and sugar until light and fluffy using a food processor, electric hand whisk, or a wooden spoon and some elbow grease. Add the eggs, one at a time, plus sour cream, self-raising flour and salt, and whisk together until smooth.
3. Spoon 900g of the mix into the 20cm square tin and put to one side.
4. Divide the remaining mixture into three bowls, with approximately 450g of cake mix in each. Colour one bowl’s mixture with the blue dye, another with the red and finally, yellow. You want the colours to be vivid, so really go for it.
5. Spoon the different coloured mixtures into the three separate loaf tins and place in the oven, along with the square tin, for 45-50 minutes, until an inserted skewer comes out clean. (You might want to rotate the tins so that they’re evenly cooked.) Leave to cool, then transfer to wire racks.
6. Meanwhile, make the ganache, which you will use to stick the cake together and coat the outside. Put the chocolate into a bowl and heat the cream in a saucepan over a medium heat. Just before it boils, pour it over the chocolate. Leave to sit for five minutes, then stir until smooth. Leave to cool.
7. Place the cooled cakes on a chopping board. Using a bread knife, slice all the edges off the cakes so that you’re left with long, brightly coloured rectangles, approximately 18cm in length.
8. Using a picture of your chosen Mondrian for inspiration, very carefully measure and slice the cakes to make straight-edged long rectangles. Put the cake slices together as you build your picture.
9. Line two trays with baking parchment. Piece by piece, spread the cake lengths with the chocolate ganache, using it like glue to stick your strips back together to recreate your Mondrian on one tray. Put in the fridge to firm up for about one hour – this hardens the ganache and makes the cake easier to work with.
10. Remove the cake from the fridge. Spread the ganache over the cake, using a pallet knife to smooth it over the sides and top. Transfer to the fridge for one hour to firm up. Remove from the fridge, place the second lined baking tray on top and invert the cake. Use the rest of ganache to coat the remaining edge – you may have to heat it up slightly to loosen it. Make sure the ganache is evenly spread. Place in the fridge for a final hour, then remove and allow it to reach room temperature. Finally, slice the cake, feel smug and serve.