Preheat oven to gas Mark 5 / 190C / 375F. Grease a 20cm square cake tin. Using some baking parchment to separate the 2 mixtures means you can save time and gas in the oven and bake both mixtures at the same time. Use the baking parchment to line the base of the tin and create a 3-4 inch fold in the middle to separate the 2 mixtures.
Mix the butter, sugar, eggs, flour and vanilla together.
Split the mixture in half. Add the passionfruit curd to one half and the raspberry curd to the other half.
Place one half of the mixture in one side of the tin and the other half on the other side ensuring the baking parchment separates them.
Bake in the centre of the oven for 25 minutes or until cooked through.
Turn out and leave to cool completely.
Lay one sponge on top of the other and cut off any crusty edges.
Cut them to ensure they are the same size.
Cut lengthways so you end up with 4 rectangles.
Warm up the jam and put through a sieve.
Brush the jam along one of the long sides of sponge. Stick to a sponge of the opposite colour. Repeat with second layer and add jam between the 2 layers and stick together.
Cover an area with icing sugar to roll out the marzipan to around 40 x 20cm.
Cover the top edge of the cake with jam and place onto the marzipan. Cover the rest of the cake with the jam and fold the marzipan around so that the join sits at the bottom. Press the edges of the join together firmly before placing up the right way.