In a large bowl, cream butter and sugar until light and fluffy, 5-7 minutes. Beat in the eggs, bananas and vanilla. Combine the flour, baking soda and salt; stir into creamed mixture just until blended., Transfer to a greased 15x10x1-in. baking pan. Bake at 350° for 20-25 minutes or until a toothpick inserted in the center comes out clean. Cool in pan on a wire rack., For frosting, in a small bowl, beat cream cheese and butter until fluffy. Add confectioners' sugar and vanilla; beat until smooth. Frost bars.