Grease and flour a 10"x15" jelly roll pan. Set aside. Preheat oven to 375 degrees.
In a large bowl, beat together, sugar, sour cream, butter and eggs until creamy. Blend in bananas and vanilla. Add flour, baking soda and salt. Blend for 1 min. Stir in nuts (optional).
Spread batter evenly into pan. Bake 20-25 min. or until golden brown.
Frosting: heat butter in sauce pan over medium heat until boiling, letting butter turn slightly brown. Remove from heat immediately. Add powdered sugar, vanilla and milk. Whisk until smooth. Should be thicker than glaze but thinner than frosting. Spread over warm bars. Let cool, cut and serve.