1
Preheat oven to 350 degrees. Butter a 9-by-5-by-3-inch loaf pan, and set aside. Whisk together the flours, flaxseed, salt, baking powder, and baking soda in a medium bowl, and set aside.
2
Put egg and egg white in the bowl of an electric mixer fitted with the paddle attachment, and mix on medium-low speed until well combined, about 2 minutes. Add melted butter, sugar, vanilla, and bananas, and mix until combined. Add the reserved flour mixture, and mix on low speed until well incorporated, about 10 seconds. Stir in walnuts.
3
Pour batter into buttered pan. Bake until golden brown and a cake tester inserted into the center comes out clean, about 35 minutes. Let cool slightly in pan on a wire rack. Invert bread to unmold; reinvert, and let cool completely on rack.
