Preheat oven to 350°F (175°C). Line a muffin pan with silicone or paper liners.
In a large bowl, mix almond flour, erythritol, baking powder, salt, and lemon zest.
In a separate bowl, whisk eggs, melted butter (or coconut oil), vanilla extract, and apple cider vinegar.
Combine wet and dry ingredients until a thick batter forms.
Gently fold in blueberries.
Scoop batter evenly into 9 muffin cups.
Bake for 20–25 minutes or until the tops are golden and a toothpick comes out clean.
Let muffins cool in the pan for 5–10 minutes before transferring to a wire rack.