| 2 1/4 cups all-purpose flour 2 teaspoons baking soda 1/2 teaspoon salt 1/2 cup butter 2 1/2 cups packed brown sugar 3 eggs 1 1/2 teaspoons vanilla extract 3 (1 ounce) squares | unsweetened chocolate, melted 1 cup sour cream 1 cup boiling water 1/2 cup butter 1 cup packed brown sugar 1/4 cup milk 1 3/4 cups confectioners sugar |