Preheat the oven to 350 degrees. Grease 2 round, 9” layer cake pans and line the bottoms with paper. Melt the chocolate in the ½ cup of water over very low heat, stirring until melted. Cool completely. Meanwhile, measure the sifted flour, baking soda, salt and baking powder and sift together. Cream the butter and sugars until light and fluffy; add the eggs, one at a time, mixing well after each addition. Blend in the vanilla. Combine the cooled chocolate with the sour cream and mix well. Add alternately with the flour mixture to the butter-egg mixture, beating well after each addition.
Pour the batter into the 2 prepared pans and bake for 30 to 35 minutes. Cool in the pans for 10 minutes and then turn out of the pans onto wire cooling racks and cool completely. If desired, frost with chocolate-sour cream frosting or chocolate-butter frosting when completely cooled.
Source: “Baker’s Chocolate and Coconut Favorites”, General Foods Kitchens, 1962