Heat oven to 375 degrees. Grease 15 x 10 inch jelly pan or 9 x 13 pan. (I used a 9 x 13 pan).
For the bars, cream together sugar, Greek yogurt, butter and eggs in large bowl. Blend in bananas, vanilla extract, flour, baking soda, and salt. Mix until batter is well blend. Stir in walnuts.
Spread batter even into pan. Bake for 25 – 30 minutes or until golden brown.
For frosting, heat butter in sauce pan over medium heat until boiling. Continue to bowl until brown turns a light brown, about 3 minutes.
Remove sauce pan from heat and add powdered sugar, vanilla extract, and milk. Mix together until smooth.