Preheat oven to 350° F. / In a mixing bowl, cream together butter and sugar. Once combined, beat in eggs, mashed bananas, and vanilla. / In a separate bowl, combine flour, baking soda, and salt. Mix flour mixture into creamed mixture until combined. Pour mixture into a greased 15″ x 10″ x 1″ baking pan / Bake for 25 minutes or until bars test done. Let cool. / In a mixing bowl, cream together butter and cream cheese. Gradually add confectioners sugar and vanilla; beat well. Spread over bars.