In a sauce pan combine butter, margarine, coffee and cocoa stir until boiling.
Pour boiling mixture over the flour and sugar. Add buttermilk, eggs, baking soda and vanilla. Mix well
Pour into a buttered baking pan if using a rectangle cake pan also use an 8X8 pan or use a jelly roll pan. (I never invested in the jelly roll pan so I just made it in 2 pans.)
Bake at 400 degrees for 20 minutes or until a toothpick comes out clean.
While brownies are baking prepare frosting. In a saucepan combine butter, cocoa and milk and heat to boiling. Remove from hear and mix in powdered sugar and vanilla until smooth. Pour over brownies as soon as you take them out of the over. Cut into bars and enjoy.