In a large bowl, beat 1/2 cup butter or margarine and 2 1/2 cups brown sugar until well mixed.
Add eggs one at a time. Beat in the vanilla and melted chocolate squares.
Add 1/2 the sour cream and then 1/2 the dry ingredients to the butter mixture until well blended.
Add the remaining sour cream and dry ingredients to the batter. Stir in hot coffee
Bake in a greased and floured 9 X 13 inch pan for 35-40 minutes or until toothpick comes out clean
Let cool 10 minutes before icing.
Sift the powdered sugar and the cocoa powder together in a large mixing bowl.
Pour in the melted butter and the coffee and mix together.
Using a wire whisk,whip it together until it becomes fluffy and smooth, about 3 or 4 minutes.
Adjust Powdered Sugar in frosting for desired consistency
Look on back of bakers chocolate for ounce conversion