I've always liked Battenberg cake - squares of sponge held together with jam and all wrapped in marzipan. But the colours, yellow and pink, well, not a good combination at all. So I decided to make a version based on the paintings of Piet Mondrian.
Line a loaf tin with greaseproof paper and spoon in the uncoloured batter. Smooth the top of it with a palette knife. Take a second loaf tin, and cut two pieces of thin card to act as dividers. Wrap them in greaseproof paper (see the video if this makes no sense to you!). Spoon the different coloured batters into each compartment.
Put both loaf tins into the oven and bake for 25 minutes. Do not open the oven during this time. When the sponges are done (a skewer inserted into the centre should come out dry), switch off the oven, leave the door ajar and let the sponges slowly cool down.
Place the block of sponges upside down near the centre of the marzipan strip. Carefully lift one end of the marzipan up the side and over onto the top. Moisten the unjammed overlap margin with a little water. Lift the marzipan up and over and gently press the edge down to form a seam.
Refrigerate the cake for half an hour or so, and trim any overhanging marzipan from the edges. Congratulations, your cake is finished!