Preheat and prep: Set your oven to 350°F (175°C).
Line a 12-cup muffin tin with paper liners or grease it well.
Combine dry ingredients: In a large bowl, whisk together almond flour, rolled oats, coconut sugar, baking powder, baking soda, salt, and cinnamon. Break up any lumps in the almond flour with the whisk for an even mixture.
Mix the wet ingredients: In a separate bowl, whisk eggs, milk, oil, and vanilla until smooth and slightly frothy.
Bring the batter together: Pour the wet ingredients into the dry. Stir with a spatula just until combined.
The batter will be thick and spoonable, not runny.
Fold in mix-ins: Gently stir in your chosen add-ins. Avoid overmixing to keep the muffins light.
Portion the batter: Divide evenly among the muffin cups, filling each about 3/4 full. Sprinkle with optional oats and turbinado sugar for a crunchy top.
Bake: Place on the middle rack and bake for 18–22 minutes.
Muffins are done when the tops are set and lightly golden, and a toothpick comes out mostly clean with a few moist crumbs.
Cool: Let the muffins rest in the pan for 5 minutes, then transfer to a wire rack to cool completely. This helps them set and prevents sogginess.