Mix the baking-powder with the flour and sift them. Rub the butter and sugar together to a cream and beat into it the egg; then add the milk, in which the salt has been dissolved. Add the flour; beat well together and turn into a cake-tin having a tube in the center. Bake about twenty-five minutes in a moderate oven. Turn it onto a flat dish, leaving it bottom side up. The chocolate sauce given below is recommended, but any other sauce may be served with it.
Melt the chocolate on a dry pan; add the sugar and boiling water. Stir until well dissolved and smooth, then add the vanilla.