In a large bowl, stir the butter until frothy. Add both types of sugar and mix well. Add egg, egg white and vanilla flavor and stir in. Stir in the mashed bananas on the highest level of the mixer for about 30 seconds. Now mix the flour, baking soda, salt and baking powder together. Add this mixture and the cream to the butter mixture. Add the walnuts and stir in. Put the dough in a loaf pan lined with baking paper or greased.
Put in the hot oven and bake for about 75 minutes. Do a chopstick test!