Line a 6-muffin tin with paper liners or spray with non-stick spray.
Preheat the oven to 350 degrees Fahrenheit.
In a medium bowl mash bananas with a fork or potato masher until pureed.
Add melted butter, sugar, vanilla and egg and stir together until smooth.
Add dry ingredients: flour, baking powder, baking soda, cinnamon, flax seed and salt. If you want to, you can whisk dry ingredients in a small bowl before adding to the banana mixture.
Stir with a silicone spatula or wooden spoon until just combined. Don’t over mix.
Use a ⅓-cup measuring cup to scoop the batter into the 6 muffin cups.
Bake for 25 minutes or until a toothpick comes out clean.
Cool on a wire rack for at least 30 minutes before enjoying!
