Few people bake cakes from scratch anymore unless they can produce something that's not possible with a mix. This sourdough chocolate cake falls in that category. It's got a fudge-like quality you can't get any way except with sourdough and since it's all mixed in one bowl, it's almost as easy as a boxed cake.
Put the starter in a large bowl, cover loosely and allow to stand at room temperature until active and bubbling -- at least one hour. Then add the rest of the ingredients, in the order given, beating well after each addition. It is not necessary to sift or premix any of the ingredients as long as you are careful to get the baking powder and soda evenly mixed.
Grease and flour two 9-inch round cake pans, pour in the batter, which will be thin, and bake in a preheated 350. oven for about 30 minutes, or until the layers test done when poked with a toothpick. The cake will have pulled away from the sides of the pan.
Allow to cool about 10 minutes before removing from pans, then finish cooling the layers on wire racks. Do not frost until the cake is completely cold.
A mild chocolate butter cream frosting is nice with this cake.
From: Pitzer, Sara _Baking with Sourdough_ Garden Way Publishing, 1980. ISBN 0-88266-225-2 ph.