Preheat the oven to 190°C.
Grease a 20cm square cake tin with butter.
Create a central division in the tin using a folded 30cm x 20cm strip of parchment.
Line the tin with the parchment while maintaining the middle fold.
Pulse butter, sugar, eggs, flour, and vanilla in a food processor.
Divide the batter equally into two separate bowls.
Fold red food colouring into one bowl of batter until blended.
Spoon the two batters into separate sides of the tin and smooth the tops.
Bake for 25 minutes, cool briefly, and transfer to a wire rack.
Trim crusty edges and cut each sponge lengthways into two equal rectangles.
Warm the apricot jam and strain it through a sieve.
Brush sponge sides with jam and join contrasting colors together.
Stack the pairs into a checkerboard pattern and coat the outside with jam.
Roll marzipan on icing sugar to a 40cm x 20cm rectangle, 5mm thick.
Place the cake on the marzipan and brush the base with jam.
Wrap the marzipan tightly around the cake and seal the edges.
Position the cake seam-side down and trim the ends before serving.