2 Line the base of a 20x30 cm sponge roll tin with greaseproof or baking paper and grease lightly.
3 Soften the butter, add sugar and beat with a wooden spoon until well combined.
4 Add egg and beat in thoroughly.
5 Sift flour, cocoa and baking powder together and stir into liquid.
6 Stir in chosen addition (or leave out if preferred).
7 Spread into prepared tin.
8 Bake for 20 minutes. The top will be set but the mixture will appear softish.
9 Cool in tin.
This can then be iced, drizzled with chocolate or dusted with icing sugar. When topping is set, cut with a sharp knife into squares or bars.
