In a large mixing bowl beat the butter with an electric mixer on medium to high speed for 30 seconds. Add the granulated sugar and beat until light and fluffy, about 2 minutes. Beat in eggs, one at a time, on medium speed until combined. Beat in 2 teaspoons vanilla. Add flour mixture and buttermilk alternately to the beaten mixture, beating on low speed after each addition until combined. Fold in banana mixture. Divide batter between prepared pans. Bake for 35 minutes or until a toothpick inserted near the centers comes out clean. Remove and cool in pan on a wire rack for 10 minutes. Remove from pans and cool completely on the wire racks.