Cream together the butter or margarine
and sugar until pale and fluffy. Gradually beat in the egg, then fold
in the flour. Divide the mixture between 12 paper cake cases (cupcake
papers) set in bun tins (patty pans). Bake in a preheated oven at
160°C/325°F/gas mark 3 for 15–20 minutes until risen and springy to
the touch. Leave to cool.
Blend together the icing sugar and warm water. Color one-third of the
icing (frosting) with food coloring of your choice. Spread the white
icing over the cakes. Pipe the colored icing in lines across the cake,
then draw a knife point at right angles to the lines first one way,
then in the other direction, to create a wavy pattern. Leave to set.