Preheat the oven to 160°C fan/170°C/320°F/gas 4.
Grease the Battenberg tin really well with butter, then coat it with flour. If using a square cake tin, grease and line it with non-stick baking parchment. Fold a pleat down the centre of the parchment (it should look like an upside-down T shape) and use the parchment to divide the tin into two halves.
Pulse the pistachio kernels in a food processor until very fine. Alternatively place them in a bag and hit them with a rolling pin until finely crushed.
Weigh your empty mixing bowl and make a note of it. In the mixing bowl, cream together the butter and sugar until pale and fluffy; this takes about 5 minutes in a kitchen mixer fitted with a paddle, or a little longer with a hand mixer.
Slowly add the eggs to the creamed butter and sugar, along with 1 tablespoon of the flour, mixing all the time until incorporated. Fold in the remaining flour until well mixed.
Weigh the mixing bowl and subtract the weight of the empty bowl. You can now work out how much mixture you have. Place half of the mixture into another bowl.
Fold the ground pistachios and a hint of green colouring into one half of the mixture until well blended and evenly coloured. Add the rose water (or vanilla essence) and a hint of the pink colouring to the other half of the mixture and fold in until well blended and evenly coloured. Place the pink mixture in one half of the tin and the pistachio mixture in the other half.
Bake for 30–35 minutes until well risen and a skewer inserted in the centre comes out clean. Remove from the oven and leave to cool completely in the tin.
Lightly dust your work surface with icing sugar and roll out the marzipan to about 3mm thick. You need a piece about 35 x 25cm to cover the cake.
Remove the two sponges from the tin. Cut each sponge in half lengthways. Gently warm the strawberry jam in a small pan or the microwave. Use the warmed jam to stick together the four strips of cake to make a chequerboard effect.
Trim one long side of your marzipan straight, using a ruler and knife. Brush the top and sides of the assembled cake with jam and place upside down on the straight edge of your rolled-out marzipan. Brush the bottom of the cake with jam and now roll the cake over until completely covered in marzipan.
Trim away the excess marzipan and trim the ends of the cake using a sharp serrated knife. Place on your presentation plate and enjoy.
This recipe is from Bake it Great by Luis Troyano, published by Pavilion. Recipe photography by Clare Winfield.