Preheat the oven to 350°F. Line a mini-muffin pan with mini 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, lemon zest, oil, 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.
Pour batter evenly into prepared muffin pan—filling each cup all the way to the top for big, round tops, and ¾ of the way for a larger quantity of smaller muffins. Bake for 13-19 minutes. Mine took 18 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 30 minutes. Then, gently lift muffins out of the pan and place directly onto a cooling rack to cool for 20 more minutes. Enjoy immediately, or cool completely for about 1 hour before storing. Storing instructions below.
Storing Instructions: Store in an airtight container for up to 1 week in the refrigerator, or in a cool, dark environment for 3 days.To Freeze: Store in an airtight container or bag, unglazed, 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 10-second increments until just warm.