2 sticks (1 cup) butter
1 cup water
1/4 cup plus 2 tablespoons cocoa powder, divided
2 cups all-purpose flour
2 cups granulated sugar
1/2 cup sour cream
1 teaspoon baking soda
1/2 teaspoon salt
1/4 cup (1/2 stick) margarine
3 tablespoons milk
1 (16-ounce) box confectioners' sugar
1/2 teaspoon vanilla extract
1. In a small saucepan, combine the butter, water, and 1/4 cup cocoa powder over low heat. Remove from heat and pour into a large heat-resistant bowl to cool.
2. Add flour, granulated sugar, eggs, sour cream, baking soda and salt; beat until well combined then pour into a 10" x 15" rimmed baking sheet.
3. Bake 25 minutes, or until a knife inserted in the center comes out clean; set aside to cool.
4. In a small saucepan, make frosting by melting margarine with milk and remaining 2 tablespoons cocoa powder over low heat. Remove from heat and stir in confectioners' sugar and vanilla; mix well then frost cooled cake.
NOTE: If you want to fancy this up a bit, sprinkle the frosting with crushed chocolate sandwich cookies, broken-up pieces of your favorite chocolate candy bar, or Texas-sized whole shelled walnuts!