Preheat the oven to 350F. Line a 9-inch loaf pan with parchment paper and set aside.
In a small mixing bowl, combine almond flour, coconut flour, baking powder, cinnamon, and salt; mix well.
In a separate larger bowl, combine butter, cream cheese, erythritol, and stevia, mixing until smooth. Add in the eggs, one at a time, then milk and banana extract, mixing until well combined. The mixture will look curdled, but that’s alright.
Add dry mixture to wet and mix well, until combined. Fold in nuts (if using), then transfer to the lined pan. Cover the pan completely in aluminum foil.
Bake the banana bread for 45-50 minutes, removing the tin foil around the 40 minute mark, to allow top to brown. Remove from the oven once the center is mostly set.
Let the bread cool in the pan completely, before slicing.