Chocolate Sheet Cake

 Ingredients

1 cup butter (2 sticks)
1 cup water
4 Tablespoons cocoa
2 cups all-purpose flour
2 cups white sugar
1/2 teaspoon salt
2 eggs
1/2 cup sour cream
1 teaspoon baking soda


Frosting:
1/2 cup butter (1 stick)
6 Tablespoons milk
4 Tablespoons cocoa
4 1/2 cups sifted powdered sugar 
1 teaspoon vanilla extract
1 cup chopped walnuts


Directions
Preheat oven to 400 degrees F (190 degrees C).
In a large saucepan, bring 1 cup butter, water and 4 Tbs. cocoa to a boil. Remove from heat, and pour into a mixing bowl. Next, stir in flour, sugar, salt. Add eggs, sour cream, and baking soda and stir until smooth. Pour batter into a greased 10x15-inch baking pan or jelly roll pan or cookie sheet with tall sides.

Bake for 20 to 22 minutes, or until cake tests done. Cool for 20 minutes.

While cake cools, mix frosting:
Combine 1/2 cup butter, milk and 4 Tbs.cocoa in a saucepan; bring to a boil. Remove from heat. Mix in sugar, and vanilla. Stir in walnuts. Spread frosting over warm cake.