Preheat the oven to 350°F (176°C). Line an 8.5-by-4.5-inch loaf pan with parchment, leaving paper over the sides.
Whisk the almond flour, coconut flour, baking powder, cinnamon, xanthan gum, and sea salt together.
Beat the softened butter and monk fruit allulose blend until fluffy.
Beat in the eggs one at a time, then mix in the almond milk and banana extract.
Add the dry mixture gradually to the wet mixture while mixing on medium speed.
Stir in 3/4 cup of the chopped walnuts.
Transfer the batter to the prepared pan, smooth the top, and scatter over the remaining walnuts.
Bake for 30 to 40 minutes until golden. Cover with foil, then bake for another 20 to 25 minutes, until a toothpick comes out clean.
Cool the loaf completely before lifting it from the pan and slicing.