Fortnum's Battenberg

Melt the butter over a low heat and set aside. Sift the flour into a bowl. In another bowl, whisk the eggs and sugar with an electric beater until pale, thick and greatly increased in volume, thick enough to leave a trail when the whisk is lifted. Sift the flour over in three additions, folding each in with a large metal spoon and knocking out as little air as possible. Drizzle the melted butter round the edge and fold that in too.

Put half the mixture in a second bowl. Split the vanilla pod, scrape the seeds into one bowl and fold them in with a drop of yellow colouring. Fold a drop of red colouring into the other to make it pale pink.

Butter and flour a Battenberg tin and spoon the pink mixture into two sections and the yellow into the others. Without a Battenberg tin, use a rectangular tin about 20 by 16cm with a strip of waxed card down the middle, pink one side and vanilla the other. Bake in an oven heated to 160 °C (gas 3) for 20 minutes, until well risen and a skewer comes out clean. Cool in the tin.

Run a knife round the tin and along the dividers and lift out the cakes. Trim the tops flat if needed. From an ordinary tin, cut each piece in half lengthwise: you need four long blocks exactly the same size.

Warm the apricot jam and sieve it. Brush jam along a long side of one pink and one yellow block and press them together. Brush the tops with jam and lay the other two on top in a chequerboard, sticking them with jam. Trim the sides if they do not line up.

Dust the work surface with icing sugar and roll the marzipan into a rectangle about 4mm thick, as wide as the cake is long and long enough to wrap round it. Neaten the edges and brush with the rest of the warm jam.

Put the cake at one end of the marzipan and roll it up, smoothing the marzipan on as you go. Trim the surplus, seal the join and set it join down. Brush off any icing sugar, trim the ends and score the top lightly in diamonds.