Chocolate Sheet Cake is a quick and always-popular dessert with a frosting that turns to fudge. Terrific for a summer picnic.
Preheat the oven to 350 degrees F. Grease an 11-inch by 17-inch baking pan.
In a large saucepan, combine the 1 cup butter, ¼ cup cocoa, and water. Bring to a boil, then cool to room temperature. Add the remaining cake ingredients and beat until smooth. Pour into the prepared pan. Bake for about 22 minutes or until a tester inserted near the center comes out clean.
Meanwhile, make the frosting by combining all the ingredients in a saucepan. Bring to a boil. Pour the warm frosting on the warm cake. Let cool before serving.