Preheat oven to 350 degrees. Grease or line a 12-cup muffin tin with paper liners, set aside.
In a large bowl, whisk both flours, sugar and baking powder together very well. Make a well in the center and add melted coconut oil, melted butter, eggs, vanilla greek yogurt and milk. Gently fold ingredients into one another by hand with a rubber spatula and just before all ingredients are almost completely combined, fold in blueberries and continue to fold until evenly distributed throughout the batter. Be extremely careful not to over-mix (this is what causes tough muffins!) Batter will be very thick.
Distribute the batter throughout the prepared muffin tin liners, ¾ to the top. If you are using turbindo sugar, sprinkle on top of the muffins at this point. Bake muffins for 18-20 minutes or until a toothpick inserted in the center comes out mostly clean with a few moist crumbs but NO wet batter. Allow muffins to cool for 3-5 minutes in pan or until you can handle them without burning yourself and transfer onto a wire rack to finish cooling completely or serve warm (the best!).
Lightened-up Blueberry Muffins will stay fresh for up to 3 days stored in an airtight container at room temperature.