Instructions: Butter a 9- by 13- by 2-inch metal pan and line the bottom with parchment or buttered waxed paper, cut to fit. Set a rack at the middle level of the oven and preheat to 350 degrees.

Combine the flour, cocoa, baking powder and baking soda in a mixing bowl and stir well to mix. Sift the dry ingredients onto a piece of parchment or waxed paper and set aside. Beat the butter and sugar together in an electric mixer set at medium speed. Beat in the eggs, one at a time, beating smooth after each addition. Lower mixer speed to low and beat in half the dry ingredients. Scrape bowl and beaters well. Add the sour cream and scrape again, then beat in the remainder of the dry ingredients.

Scrape batter into prepared pan and bake cake 40 to 45 minutes, or until well risen and a toothpick or knife inserted into the center of the cake emerges clean. Cool in pan on a rack for 5 minutes, then turn out of pan. Turn cake over again so it stands right-side up to finish cooling.

This recipe yields 12 servings.

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