In medium bowl, mix flour, 2/3 cup cocoa, the baking soda, coffee powder and 1 teaspoon salt; set aside. In large bowl, beat 1/2 cup butter and the granulated sugar with electric mixer on medium speed until light and fluffy. Beat in eggs and 1 teaspoon vanilla. Alternately add flour mixture with buttermilk, beating on low speed until smooth. Divide batter evenly among muffin cups, using about 1/3 cup in each.