Chocolate Brownie Sheet Cake

Originally found on gfingf.blogspot.com
This cake sounds really easy and yummy. I'll let you know when I try it.

Chocolate Brownie Sheet Cake

Mix together 2 cups gf flour and add1 tsp xanthan gum and 2 cups sugarBring to boil: 2 sticks butter, 4 Tbs cocoa, 1 cup waterThen pour that over flour and sugar mixture and add 2 eggs (I added 2 extra egg whites per baking tips you sent me) 1/2 tsp salt, 1 tsp baking soda, 1/2 cup buttermilkBeat well and bake @ 350 degrees for 20 min in a 9 by 13 pan. Now for the icing (which is the best icing ever!) :Melt 1 stick butter, 6 Tbs milk, 4 Tbs cocoa, and add 1 cup chopped pecans.Bring to a boil, remove and add 1 lb of powdered sugar. Pour immediately over the hot cake.