Aunt Sherry's Texas Sheet Cake

My husband's favorite after school cake from childhood made by his favorite aunt. He would go to Aunt Sherry's house after kindergarten and there she would serve him the unheard of treats at home of  Dr. Pepper and sheetcake (or a whole array of Hostess products).  At home, if there was a treat he had to compete with several older brothers and being so much younger he only got the crumbs. Aunt Sherry's was a special place for him to receive that one on one attention and as he says "she drew the short straw and had to take care of him," though I don't think she saw that way.
. 
Texas Sheet Cake
Preheat Oven 375°F
2 sticks 1/2 pound butter
1 cup water
5 tablespoons cocoa
2 cups sugar
2 cups flour
½ teaspoon salt
½ cup sour cream
2 eggs
1 teaspoon baking soda
1 teaspoon cinnamon
1 teaspoon vanilla

In a large bowl, whisk together, flour, sugar, baking soda, salt, and cinnamon. Set aside.
In a medium saucepan over medium heat combine butter, water and cocoa.
Bring to a boil whisking out lumps.
Remove from heat.
Add dry ingredients to the saucepan and mix with a hand held electric mixer.
Add the sourcream, eggs and vanilla mixing until combined.
Spread onto a large ungreased non stick cookie sheet.
Bake for 20-25 minutes.

Chocolate Icing
While the cake is baking prepare the icing:
1 stick ¼ pound butter
6 tablespoons milk
4 tablespoons cocoa sifted if lumpy
1 pound powdered sugar
1 teaspoon vanilla

Sift powdered sugar to remove lumps and set aside.
In a medium saucepan add butter, milk, and cocoa and bring to a boil whisking until smooth.
Remove from heat and add powdered sugar and vanilla to the saucepan.
Mix with electric mixer until smooth.
Ice the cake immediately after removing from the oven.
Top with chopped walnuts or pecan, raw or browned in a pan or oven.
Cake freezes well.