From 1912:

Cream a lump of butter the size of an egg with a cupful of sugar, add one-half cupful of milk and one-half cupful of water. Sift together three times one and one-half cupfuls of flour and a teaspoonful of baking powder and add to the other ingredients. Last of all, fold in the stiffened whites of two eggs. Bake in a very moderate oven. If gas is used, do not heat the oven until the cake is in. Make a boiled frosting, cover the cake with it, let it cool, then pour over this unsweetened chocolate that has been melted over steam. A pinch of cream of tartar in the boiled frosting will improve it.