Butter and flour a square baking pan. Sift together dry ingredients. Melt butter in a double boiler; add chocolate and melt. Beat together eggs, sugar and vanilla. Stir in chocolate mixture until well combined. Add dry ingredients. Add sour cream.
Place batter in prepared pan and bake at 325 degrees Fahrenheit for 40 minutes.
Variations Macadamia chocolate chunk Add 4 ounces semisweet chocolate (cut into 1/4 inch chunks) to the batter. Add another four ounces semisweet chocolate to the top, along with 1 1/2 cups raw, unsalted macadamia nuts. Add 10-15 minutes to the cooking time.
Peanut-Raisin Add 1 1/2 cups raisins to the batter. Spread 1 1/2 cups unsalted peanuts on top. Add 10-15 minutes to the cooking time.
Hazelnut Brownie Cake Pour 1 recipe of the basic brownie into a 9-inch cake pan, and bake as directed above.
1 1/2 cups heavy cream 12 ounces semisweet chocolate 1 cup chopped, toasted hazelnuts
In a double boiler, melt chocolate into boiling cream to form a ganache. Pour 1 cup of ganache over 1 cup chopped hazelnuts. Cut cake in half and spread hazelnut-ganache mixture in between the layers. Pour plain ganache over cake as an icing. Pipe ganache which has been refrigerated for 10-15 minutes onto the cake in the form of stars as decoration.