Preheat an oven to 180°c/160°c fan (355°f/320°f).Grease the Battenberg tin then line each section with baking parchment. Place the sugar into the bowl of a stand mixer then rub in the lemon zest. Add in the softened butter then use the paddle attachment to beat the butter until light & fluffy, around 4-5 minutes.
With the mixer running on a medium speed, beat in the eggs one at a time.
Sift together the flour & baking powder then fold into the batter along with the ground almonds, salt, vanilla & almond extract.Once mixed, fold in the lemon curd. Weigh the batter then divide equally into 2 bowls.
Take one half of the batter & divide between 2 sections of the tin.
Take a spoonful of batter from the other bowl & place into a separate bowl, stir in a couple of drops of food colouring (the batter should be a dark pink colour) then fold back into the batter. Divide the pink batter into the remaining 2 sections of tin.
Use a palette knife to level off each section of batter (wash your palette knife before using on the other colour batter).
Place the tin onto a baking tray & bake in the preheated oven for 20-25 minutes or until risen & a skewer inserted into the cake comes out clean.
Leave to cool in the tin for 30 minutes then use a sharp, serrated knife to trim the top of the cake so that it is level with the top of the tin.
Carefully remove each section of cake from the tin then peel off the baking parchment & transfer to a wire cooling rack to cool completely.