We made a rather delicious birthday cake for one of our friends, and it worked so well I thought I'd post it here (because I'm bound to lose the piece of scrap paper it's scribbled on).
Preheat oven 180° C. Whisk eggs. Cream butter and sugar together. Sift in flour and baking powder. Mix cocoa powder and 3 tbsp hot water together to form a paste, and stir in. Add 1 tbsp milk if still stiff. Put in greased 8 in sprung cake tin and bake for 35-40 minutes.
Place cocoa and butter in bowl and microwave on 800 W for 20 seconds. Cream together, and gradually sift in sugar. Add a small amount of milk if too thick. Spread on cake once cool.
