In a mixing bowl, cream butter, and sugar.
Beat in eggs, bananas, and vanilla.
Combine the flour, baking soda, and salt.
Add to creamed mixture, and mix well.
Pour into a greased 15 X 10 X 1 baking pan.
Bake at 350º for 22 to 25 minutes.
Cream butter, and cream cheese in a mixing bowl. Add gradually the powdered sugar, and vanilla.
Spread over bars.