Heat the oven to 180C/160C fan/gas 4. Butter a 20cm square tin. Cut a sheet of non-stick baking parchment into a 40 x 20cm rectangle. Fold in half, so the short ends meet, then lower into the middle of the tin, ensuring the fold sticks up to divide the tin into two equal parts, each measuring 20 x 10cm. The parchment should overhang a little on two sides.

Beat the butter and sugar in a stand mixer or in a bowl using an electric whisk for 5 mins until pale and fluffy. Add the eggs one at a time, adding a tablespoon of the flour with the last egg to prevent curdling. Carefully fold in the rest of the flour using a metal spoon.

Scrape half the cake mixture into a separate bowl. Add the ground pistachios to one of the bowls along with the green food colouring and 1-2 tbsp milk and mix to combine. The mixture should form a dropping consistency. If it is too stiff, add a drop more milk. Add the ground almonds to the other bowl of mixture along with 1-2 tbsp milk, the pink food colouring and rose essence (don’t add more than 1/4 tsp or the rose flavour will be overpowering). The pink mixture should be the same consistency as the green.

Pour the different mixtures into the different sections of the cake tin, and level the tops using the back of a spoon. Bake for 25-30 mins until a skewer inserted in the middle of each cake comes out clean. Leave to cool completely before lifting out of the tin using the baking parchment.

Level the tops of the two cakes using a serrated knife and trim the edges so that both are the same size. Slice both cakes in half lengthways to give you two long pieces of pink cake and two of green.

Spread apricot jam along the length of a green piece and a pink, then stick them together. Spread more apricot jam on top of them, and on one long side of each of the remaining pieces. Place the green piece on top of the pink and the pink on top of the green, again using the jam as glue. Brush the top of the cake with more jam.

Sprinkle icing sugar onto a clean work surface and roll out the marzipan into a rectangle large enough to enclose the cake (around 20 x 35 cm). Use the rolling pin to lift away the marzipan, then brush away the icing sugar and sprinkle the caster sugar over your work surface. Lay the marzipan on top of the caster sugar with one of the longer ends closest to you.

Carefully place the cake, jam-side down, into the middle of the marzipan, sitting lengthways, and brush the sides and top with more jam. Fold the marzipan around the cake, trimming the longer edges if you need to. Pinch the edges of the marzipan together and smooth using a knife. Tidy each end by cutting away a thin slice. Carefully turn the cake the right way up onto a serving plate and decorate with pistachios and rose petals, if using.