Heat the oven to 180 °C / 356 °F. The oven should be fully preheated before the batter goes in so the loaf starts rising right away.

Beat the eggs, mashed banana, and melted butter with an electric mixer until the mixture looks smooth and evenly blended. You should not see streaks of egg, and the mixture will look creamy and lightly thickened.

In a separate bowl, stir together the almond flour, granulated sweetener, cinnamon, and baking powder, then add the dry mixture to the wet mixture and blend until combined. The batter should look thick and scoopable, not loose or pourable.

Fold in the crushed walnuts, saving a small portion for the top. The nuts should be evenly distributed so every slice gets a little crunch.

Line a small 7 x 3.5 inch loaf tin with parchment paper and spoon in the batter, then scatter the reserved walnuts over the top. Smooth the surface lightly so the loaf bakes evenly and rises neatly.

Bake for about 40 minutes, checking at the 30 minute mark and loosely covering the top with foil if it is browning too quickly. Your kitchen will fill with the warm scent of cinnamon and banana, and a knife inserted into the center should come out clean when the loaf is done.

Set the loaf aside and let it cool completely before slicing. This is the hardest part, but patience will reward you with clean slices instead of a soft, crumbly center.