Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13 inch baking pan.
In a medium bowl, cream 1/2 cup butter and sugar until light and fluffy. Beat in eggs one at a time. Stir in the mashed bananas. In another bowl, sift together the flour, baking powder, baking soda, and salt. Stir into the banana mixture until just blended. Add the walnuts, if desired, and vanilla. Spread batter into the prepared pan.
Bake at 350 degrees F (175 degrees C) for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean. Let cool.
To Make Frosting: In a medium bowl, cream 1/2 cup butter and brown sugar. Beat in the milk. Gradually beat in the confectioners' sugar until frosting is of a spreading consistency. Spread over cooled bars.
Interesting Facts
Bananas are one of the most popular fruits in the world!
Bananas are a good source of vitamins and minerals, including potassium, vitamin C, and vitamin B6.
Bananas can be used in many desserts, including cakes, pies, and, of course, bars!