Preheat and prep: Set your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease with oil or butter.
Mix dry ingredients: In a large bowl, whisk almond flour, sweetener, baking powder, baking soda, salt, and cinnamon until evenly combined and lump-free.
Mix wet ingredients: In a separate bowl, whisk eggs, almond milk, sour cream, melted butter, and vanilla until smooth.
Combine gently: Pour the wet mixture into the dry.
Stir with a spatula just until combined. The batter should be thick but scoopable. Fold in any optional add-ins.
Fill the tin: Divide the batter evenly among the muffin cups, filling each about 3/4 full.
For taller muffin tops, fill closer to the top and use only 10 cups.
Bake: Place in the center of the oven and bake for 18–22 minutes, or until the tops are set and a toothpick comes out clean or with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely. They firm up as they cool, so resist cutting in too early.
Serve: Enjoy warm or at room temperature. Add a pat of butter or a smear of sugar-free jam if you like.