01 - 
                Preheat oven to 375 degrees F and grease a 9x13 inch pan with non-stick cooking spray.
              
              
              
                02 - 
                In a large bowl, cream together the sugar and butter. Beat in the Greek yogurt (or sour cream), eggs, mashed bananas and vanilla extract.
              
              
              
                03 - 
                Add the flour, baking soda, and salt, mixing just until moistened. If using nuts, stir them in now.
              
              
              
                04 - 
                Spread batter evenly into prepared pan and bake for 23-28 minutes or until a toothpick inserted in the center comes out clean, or with few crumbs.
              
              
              
                05 - 
                While the bars bake, heat the butter in a large skillet over medium heat. Allow it to come to a simmer until it starts to turn a delicate brown and has a nutty aroma (watch carefully to avoid burning). Remove from heat immediately.
              
              
              
                06 - 
                Whisk in the powdered sugar, vanilla extract and 1 tablespoon of milk until smooth. Add more powdered sugar or milk if needed to achieve desired consistency.
              
              
              
                07 - 
                Pour the warm frosting over the warm banana bread bars. Spread gently with the back of a spoon and allow to cool before cutting into squares.