Step 1

Heat oven to 375F. Grease and flour 15×10-inch jelly roll pan. For the bars, in a large bowl, beat together sugar, sour cream, butter, and eggs until creamy. Blend in bananas and vanilla extract. Add flour, baking soda, salt, and blend for 1 minute. Stir in walnuts(optional). Spread batter evenly into pan. Bake 20 to 25 minutes or until golden brown.

Step 2

Heat butter in a large saucepan over medium heat until boiling. Let the butter turn a delicate brown and remove from heat immediately. Make sure to watch the butter because it can easily go from browned to burnt. Add powdered sugar, vanilla and milk. Mix until smooth. Immediately spread over the cake while warm, it spreads much easier.