Preheat the oven to 350°F. Line a 12-cup muffin pan with muffin liners. Set aside.
In a large bowl, sift together all the dry ingredients: oat flour, almond flour, baking soda, baking powder, and salt.
Add water and milk to a microwave-safe bowl. Heat in 10-second increments until just warm. This will prevent the melted coconut oil from solidifying once mixed with these liquids.
In a medium bowl, whisk together all wet ingredients: water, milk, lemon juice, coconut oil, coconut sugar, maple syrup and vanilla. Whisk until well incorporated.
Add wet ingredients to dry ingredients. Whisk until just incorporated, making sure no flour patches remain. Fold in blueberries. Optionally, sprinkle and gently press small blueberries into the tops of the muffins.
Pour batter evenly into prepared muffin pan—filling each cup all the way to the top for a lower quantity of big, round topped muffins, and ¾ of the way for a higher quantity of smaller muffins. Bake for 23-29 minutes. Mine took 26 minutes. Insert a toothpick to check for doneness—once it comes out clean, it’s done.
Place muffin pan on a cooling rack to cool for 20 minutes. Remove muffins from pan and transfer to a cooling rack to cool completely, about 1-2 hours. Enjoy! Storing instructions below.
A Note on Homemade Oat Flour: *If using homemade oat flour, make sure to blend the flour until very fine and sift the flour to remove coarse bits of oats that could create less than ideal results. Store until needed, then measure the amount required for the recipe.
Storing Notes: Store in an airtight container for up to 2-4 days in the refrigerator, or in a cool, dark environment. Best on the 1st day.
To Freeze: store in an airtight container or bag, in the freezer for up to 1-2 months. Allow to thaw for about 30 minutes at room temperature before enjoying. Or, heat in the microwave in 15 second increments until just warm.