Preheat oven 350. Grease bottom only of 9x5x3 inch loaf pan.
Beat butter in large bowl with a mixer on medium speed until light and fluffy. Add brown and granulated sugar beat well. Add egg, egg whites and vanilla; beat until well blended. Add mashed bananas, and beat on high speed.
combine flour, baking soda and powder,and salt in a medium bowl. Add flour mixture to butter mixture. Alternately with heavy cream and flour mixture ending with flour.
Add walnuts to batter mix well.
Pour batter into loaf pan (evenly) Bake until brown and toothpick comes out clean.
Cook time is about 1 hour 10 minutes.
Cool in pan for about 10 minutes then remove from pan and cool completely on wire rack.