Preheat oven to 350°. In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs, sour cream and vanilla. Combine flour, baking soda and salt; gradually add to creamed mixture. Stir in bananas. , Spread into a greased 15x10x1-in. baking pan. Bake until a toothpick inserted in the center comes out clean (do not overbake), 20-25 minutes. Let cool., For frosting, in a large bowl, beat cream cheese, butter and vanilla until fluffy. Gradually beat in enough confectioners' sugar to achieve desired consistency. Frost bars. Store in the refrigerator.