Heat oven to 350°. Grease and flour a 13x9-inch pan. In a small bowl, combine 1/4 cup butter and banana until well blended. Add milk and egg; beat well. Stir in flour and remaining bar ingredients until well mixed. Spread in greased and floured pan. Bake at 350° for 20 to 25 minutes or until light golden brown.
Meanwhile, melt 2 tablespoons butter in a small saucepan. Stir in powdered sugar, lemon juice, and enough water for desired spreading consistency. Spread over warm bars. Cool completely. Cut into narrow bars and garnish as desired.