In a bowl, cream butter and sugar. Add the eggs, sour cream and vanilla one at a time. Combine the flour, baking soda and salt; gradually add to the creamed mixture. Stir in bananas.
Spread into a parchment lined 13 x 10 x 1 inch baking pan. Bake at 350° for 20-25 minutes or until a toothpick inserted near the center comes out clean. Cool.
In a bowl, beat the cream cheese, butter and vanilla. Gradually beat in enough confectioners' sugar to achieve desired consistency. Frost bars, after cake is thoroughly cooled. Store in the refrigerator. Cut into squares and enjoy cold!