One-Egg Chocolate Cake

A spiced chocolate sheet cake leavened with soda and cream of tartar rather than baking powder. The original gives quantities and nothing else, so method, pan and oven are left to the cook.

• Mix in this orderCream the butter and sugar, beat in the egg, sift the flour with the cocoa, spices, soda and cream of tartar, then add the dry mixture and the milk alternately. Soda plus cream of tartar begins working the moment it is wet, so get the batter into the pan and into the oven without delay.
• OvenNo temperature is given. Around 350F suits a sheet cake of this size.
• "Bake in sheet"A shallow rectangular pan, greased and floured. A 9x13 inch pan takes 25 to 35 minutes; a larger jelly-roll pan gives a thinner cake in about 20 minutes. Test with a skewer in the centre.
• Sweet milkPlain fresh milk. The term distinguishes it from sour milk or buttermilk, which would normally have been leavened with soda alone rather than the soda-and-cream-of-tartar pair.
• The leavening pairHalf a teaspoon of soda to one teaspoon of cream of tartar is the usual 1:2 proportion; on the standard equivalence of 1/4 teaspoon soda plus 1/2 teaspoon cream of tartar per teaspoon of baking powder, that is close to 2 teaspoons of baking powder, which can be substituted directly.
• A quarter nutmegGrated from a whole nutmeg, this is about half a teaspoon. With two teaspoons of cinnamon and a teaspoon each of cloves and allspice, the spice dominates the cocoa; three tablespoons of cocoa reads as colour and depth rather than chocolate flavour.
• The butter proportionA full cup of butter against two cups of flour and only one cup of sugar is rich, and restrained in sugar by current standards. Expect a close, rich crumb. The quantities are as printed.
• Yield and icingA 9x13 sheet cuts into 12 to 15 squares. Any plain butter icing or boiled white icing suits it; the spices take well to a little coffee or orange in the icing.