Step 1

Preheat oven to 350 degrees F. Coat a 9- x 13-inch baking dish with cooking spray.

Step 2

In a large bowl with an electric mixer, beat granulated sugar, the 1/2 stick softened butter, sour cream, and eggs until creamy. Beat in bananas and 2 teaspoons vanilla. Add flour, baking soda, and salt; mix well. Pour into baking dish.

Step 3

Bake 30 to 35 minutes, or until toothpick inserted in center comes out clean. Let cool.

Step 4

In a small saucepan over medium heat, melt remaining 1/2 stick butter. Stir in brown sugar and milk and bring to a boil, stirring constantly. Reduce heat to low and cook 2 minutes. Remove from heat and place in a large bowl. Let cool 15 minutes.

Step 5

Add confectioners' sugar and remaining 1 teaspoon vanilla to bowl and beat with electric mixer until smooth. Spread frosting over cake and serve.