Preheat oven to 350 degrees F (175 degrees C). Grease a 15x10-inch jelly roll pa.
Step 2.
Beat sugar, sour cream, softened butter, and eggs in a bowl with an electric mixer until cream. Beat in bananas and vanilla extract. Add flour, baking soda, and salt; mix for 1 min. Stir walnuts into evenly incorporated. Spread batter in prepared pan.
Step 3
Bake in the preheated oven until golden, about 27 minutes. Cool.
Step 4
Melt butter in a large saucepan over med heat until bubbling and golden brown, 3 to 5 minutes. Remove from heat.
Step 5
Whisk confectioners’ sugar , milk and vanilla extract into melted butter until smooth frosting consistency is reached. Spread frosting over cooled banana bars.