Prep the pan and oven. Heat your oven to 350°F (175°C).
Line a 12-cup muffin tin with liners or lightly grease each cup.
Make the oat flour. If using rolled oats, blend them in a blender until fine and powdery. You should end up with about 1 cup of oat flour.
Mix dry ingredients. In a large bowl, whisk oat flour, almond flour, protein powder, baking soda, baking powder, salt, and cinnamon until evenly combined.
Blend wet ingredients. In a separate bowl, whisk eggs, Greek yogurt, milk, maple syrup, melted coconut oil, and vanilla until smooth and creamy.
Combine gently. Pour the wet ingredients into the dry. Stir with a spatula just until no large streaks of flour remain.
The batter will be thick but scoopable.
Fold in blueberries. Toss blueberries with a teaspoon of oat flour if you want to prevent sinking, then fold them into the batter. Don’t overmix.
Fill the cups. Divide the batter evenly among the 12 muffin cups, filling each about three-quarters full. Add a few extra berries on top if you like.
Bake. Bake for 16–20 minutes, or until the tops are set and lightly golden and a toothpick comes out with a few moist crumbs but no wet batter.
Cool. Let muffins cool in the pan for 5 minutes, then transfer to a rack to finish cooling.
They firm up as they cool.
Enjoy. Serve warm or at room temperature. For a little extra, spread with almond butter or a smear of Greek yogurt.