Prep the oven and pan: Preheat to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease.

Toast the walnuts: Spread chopped walnuts on a baking sheet and toast for 5–7 minutes until fragrant. Cool slightly.

Mix dry ingredients: In a large bowl, whisk 2 cups almond flour, 1/2 to 2/3 cup keto sweetener (to taste), 2 teaspoons baking powder, 1/2 teaspoon salt, and 1 teaspoon cinnamon.

Combine wet ingredients: In a separate bowl, whisk 3 large eggs, 1/3 cup melted butter, 1/3 cup sour cream, and 1 teaspoon vanilla until smooth.

Bring it together: Pour wet ingredients into dry and stir just until combined. Fold in 3/4 cup toasted walnuts, reserving a tablespoon for topping.

Portion the batter: Divide evenly among the muffin cups, about three-quarters full. Sprinkle the tops with the reserved walnuts.

Bake: Bake 18–22 minutes until the tops spring back lightly and a toothpick comes out mostly clean with a few moist crumbs.

Cool: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to finish cooling. They set as they cool, so don’t skip this step.

Serve: Enjoy warm with butter, or store once fully cooled.