Texas Sheet Cake

Cake:
1 cup butter
1 cup water
5 tablespoons unsweetened cocoa powder
2 cups all-purpose flour
2 cups white sugar
1 teaspoon baking soda
1/2 teaspoon salt
1/2 cup sour cream
2 eggs

Frosting:
6 tablespoons milk
5 tablespoons unsweetened cocoa powder
1/2 cup butter
4 cups confectioners' sugar
1 teaspoon vanilla extract
1 cup chopped walnuts (optional)

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 10x15 inch pan.

Melt the butter on low in a saucepan, add the water and 5 tablespoons cocoa. Bring mixture to a boil then remove from heat. Allow to cool slightly.

Combine the flour, sugar, baking soda and salt. Beat in the sour cream and eggs. Stir cocoa mixture into the egg mixture, mixing until blended.

Pour batter into prepared pan. Bake in the preheated oven for 20 minutes, or until a toothpick inserted into the center comes out clean.

Frosting: In a large saucepan, combine the milk, 5 tablespoons cocoa and 1/2 cup butter. Bring to a boil, then remove from heat. Stir in the confectioners' sugar and vanilla, then fold in the nuts, mixing until blended. Spread frosting over warm cake.

from: Allrecipes