1Preheat oven to moderate, 180 C. Line a 12-hole cupcake tray with paper cases.
2Prepare basic butter cake mixture. Divide evenly between cases. Bake 12-15 mins until cooked when tested. Transfer to wire rack to cool completely.
3Knead icing on a cornflour-dusted surface until smooth. Divide into four portions. Tint each portion. Roll out each portion to 1 cm thick. Cut 12 bricks (1 x 2cm) and pat with fingertips to soften sharp edges. Roll out small pieces of each coloured icing into balls and attach to tops of bricks with a little buttercream. Set aside 1 hour until firm.
4Divide buttercream into four bowls. Add food colouring to each bowl. Spread three cupcakes with each colour. Arrange bricks on tops of cakes, cutting some bricks in half as shown.
Photo: Rob Shaw/Bauer