Texas Sheet Cake

Recipe modified from: http://www.geniuskitchen.com/recipe/texas-sheet-cake-13554

Ingredients:
Batter
1 cup unsalted butter, melted
1 cup water
4 tablespoons cocoa (I used 3 Tbl. of light cocoa and 1 Tbl. of dark cocoa)
2 cups sugar
2 cups all-purpose flour
1⁄2 teaspoon salt
1 teaspoon baking soda
2 eggs
1⁄2 cup sour cream
1 teaspoon vanilla

Frosting:
1⁄2 cup unsalted butter
4 tablespoons cocoa (I will modify this next next to 2 Tbs of light cocoa  and 2 Tbs of dark cocoa, as it was too sweet)
6 tablespoons milk
1 lb confectioner's sugar (powdered)
1 teaspoon vanilla
1 cup walnuts chopped (optional)

Directions:
Put m1 cup unsalted butter, 1 cup water and 4 Tbs. cocoa in a large pan and bring to a boil.
Remove from heat and add the rest of the batter ingredients (2 C sugar, 2 C flour, 1⁄2 tsp salt, 1 tsp baking soda, 2 eggs, 1⁄2 C sour cream, 1 tsp vanilla).
Mix with electric mixer until smooth.
Pour into an 11 x 16 x 1.5-inch jelly roll pan.
Bake at 350° for 20 minutes.

Frosting:
Bring 1⁄2 cup butter, 4 Tbl. cocoa, and 6 Tbl. milk to a boil.
Remove from heat and stir in 1 lb. confectioners' sugar, 1 tsp vanilla,  and (optional) nuts.
Pour on cake as soon as it comes out of the oven.