Preheat and prep: Heat your oven to 350°F (175°C). Line a 12-cup muffin pan with parchment liners or grease well. This helps prevent sticking, since almond flour can cling.
Mix the dry ingredients: In a large bowl, whisk almond flour, coconut flour, baking powder, salt, and sweetener until no lumps remain. A smooth base gives you an even crumb.
Combine the wet ingredients: In a separate bowl, whisk eggs, almond milk, melted butter (cooled), vanilla, and lemon zest. Make sure the butter isn’t hot or it can scramble the eggs.
Bring it together: Pour the wet mixture into the dry. Stir with a spatula until just combined. The batter will be thick but scoopable. If it looks dry, add 1–2 teaspoons more almond milk.
Fold in blueberries: Gently stir in the blueberries. If using frozen, add them straight from the freezer to reduce bleeding. Don’t overmix.
Portion: Divide the batter evenly among the muffin cups, filling each about 3/4 full. For a bakery look, sprinkle a little coarse sweetener on top.
Bake: Place on the center rack and bake 18–22 minutes, or until the tops are golden and a toothpick comes out clean or with a few moist crumbs.
Cool: Let muffins cool in the pan for 10 minutes, then transfer to a rack to cool completely. Almond flour muffins set as they cool, so this step matters.