Preheat your oven to 325°F (160°C). Lightly spray a 9x5 inch loaf pan with a nonstick spray.
In a medium bowl, combine the almond flour, oat fiber, baking powder, salt, cinnamon, and nutmeg. Whisk everything together until it's well blended, then set this bowl aside.
In a separate mixing bowl, use a hand mixer to whip the egg whites until they form stiff, airy peaks. This step helps give the bread a lovely light texture!
In a third, larger mixing bowl, add the egg yolks, sour cream, heavy cream, powdered sweetener, banana extract, and vanilla extract. Stir well until all these ingredients are smoothly combined.
Carefully fold the whipped egg whites into your wet mixture. Then, gradually add the dry ingredient mix to this bowl, stirring gently until everything is just combined. Be careful not to overmix!
Stir in half of the chopped walnuts by hand.
Pour the batter evenly into your prepared loaf pan. Sprinkle the remaining chopped walnuts over the top of the batter.
Place the pan in your preheated oven and bake for 35-40 minutes. You'll know it's done when a toothpick inserted into the center comes out clean.
Allow your delicious bread to cool in the pan for about 15 minutes before carefully transferring it to a wire rack to cool completely. This helps it firm up nicely. Once cooled, slice it up and enjoy your guilt-free, healthy treat!