In a mixing bowl, cream butter and sugar. Add eggs, sour cream, and vanilla.
Combine flour, baking soda, and salt in a separate bowl. Gradually add to the cream mixture.
Stir in bananas. Spread into a greased 15x10x1-inch pan. Bake at 350 degrees for 20-25 minutes or until a toothpick inserted near the middle comes out clean. Cool.
***For the Frosting***
Mix cream cheese, butter, and vanilla; mix well.
Gradually add in enough powdered sugar to achieve the desired consistency. Frost bars and store in the refrigerator.