In medium bowl, mix flour, cocoa, baking soda and salt; set aside. In large bowl, beat brown sugar, granulated sugar and 1 cup butter with electric mixer on medium speed 2 minutes or until light and fluffy. Add eggs, one at a time, beating until well blended. Add melted chocolate and 1 1/2 teaspoons vanilla, beating until blended. On low speed, alternately add flour mixture and buttermilk, beating just until blended after each addition. Beat in coffee until blended. Pour batter into pan.