275 g (10 oz) soft brown sugar
25 g (1 oz) cocoa powder
90 ml (3 fl oz) water
225 g (1/2 lb) flour
2 tsp baking powder
1/2 tsp bicarbonate of soda
1/2 spoon salt
100 g (4 oz) butter
1 tsp spoon vanilla essence
2 eggs, separated
150 ml (1/4 pint) soured cream
For the icing:
100 g (4 oz) butter, softened
225 g (8 oz) icing sugar, sifted
100 g (4 oz) plain chocolate, broken into pieces
1 tbsp milk
25 g (1 oz) chopped nuts (hazelnuts, almonds, walnuts), to finish