Preheat oven to 400º. Grease and flour sheet pan.
Combine flour,sugar,soda in bowl.
Bring butter, crisco, cocoa and water to boil.
Add liquid to dry ingredients and mix well,
Add slightly beaten eggs, butter milk and vanilla.
Bake 20 minutes.
Bring butter, cocoa, and milk to a boil, remove from heat and add powdered sugar, vanilla and nuts(if desired)
Pour over warm cake.