In a saucepan, melt butter or margarine. Add sugar and cocoa and mix well.
1 cup butter or margarine, 2 cups sugar, 10 Tbsp cocoa
Transfer to a mixing bowl, then add eggs, flour,, vanilla and salt.
4 eggs, 1 1/2 cup flour, 1/4 tsp salt, 1 tsp vanilla
Mix well, then spread in a lined 13x9. If you are using mix-ins, add them to the batter before spreading it in the pan.
Bake at 350° for 20-25 minutes.