Sift together the flour, baking soda, baking powder and salt. Set aside.
In a large mixing bowl beat 1/2 cup softened butter and 21/2 cups brown sugar. Add eggs one at a time. Add vanilla and the melted chocolate squares.
Add 1/2 the sour cream and 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 the boiling water.
Pour batter into a 9x13 inch pan. Bake at 350' in preheated oven for 35 minutes or until a toothpick inserted comes out clean. Cool before frosting with your favorite frosting. Cream cheese frosting recipe will follow. This is our favorite for most cakes.
Cream Cheese Frosting:
Beat 8 oz. of softened cream cheese with 1/2 cup of softened butter and 1teaspoon vanilla until light and fluffy.
Gradually add 2 cups of confectioner's sugar and beat well. Add the remaining 2 1/4 cups of confectioner's sugar and beat until smooth. (total 4 1/4 cups)