Combine sugar, sour cream (or yogurt), butter, and eggs. Stir in mashed bananas and vanilla. Add flour, salt, and baking soda. Spread into a greased 10x15x1 (regular sized cookie sheet) and bake at 375 degrees for 18-20 minutes or until light brown. After it has cooled, whisk butter, powdered sugar, milk, and vanilla together for the glazed topping and spread over top.