Heat oven to 180°C, 350°F, Gas Mark 4. Grease an 18 cm (7 inch) shallow square cake tin.
Cream together margarine and sugar until pale and fluffy. Gently stir in the flour, chocolate drops and cocoa. Mix well.
Press into the prepared tin and bake for about 30 minutes until firm at the edges. Leave to cool in the tin then turn out.
Make the Buttercream (see below) and spread over the top of the biscuits. Cut into 2 bars and decorate with chocolate drops and strands to look like dominoes.
Buttercream
50 g (2 oz) butter
100 g (4 oz) icing sugar, sieved
2 x 5 ml spoon (2 tsp) hot water
Beat butter until soft, gradually beat in icing sugar, water
and any flavouring.
Vanilla: Add a few drops of vanilla essence.
Chocolate: Add 1 x 15 ml spoon (1 tbsp.) sieved cocoa powder
with the icing sugar.
Coffee: Dissolve 1 x 5 ml spoon (1 tsp.) instant coffee in hot water.
Orange or lemon: Add finely grated rind of half an orange or one lemon. Replace the hot water with orange or lemon juice.