Preheat your oven to 425°F (220°C). Grease a muffin tin and set aside.
In a large mixing bowl, whisk together all of the wet ingredients until smooth and well combined. For the smoothest consistency, use a blender or food processor to puree the bananas before adding to the wet ingredients.
Add the freshly milled flour, salt, flax seed, and cinnamon to the bowl with the wet ingredients. Gently stir just until incorporated. Cover and set aside to let the flour absorb the liquid for 10 minutes.
After resting, sprinkle in the baking powder and baking soda. Mix gently until everything is evenly combined, being careful not to overmix. Fold the mix-ins into the batter.
Working quickly, spoon the batter into the prepared muffin tin, filling each cup evenly.
Bake at 425°F for 5 minutes, then reduce the oven temperature to 350°F (175°C) and continue baking for 10-12 more minutes, or until the centers feel firm and the muffins are baked through.
Remove from the oven and let cool slightly on a wire rack — or enjoy warm right away.
Store cooled muffins in an airtight container at room temperature for up to 2 days. For longer storage, freeze the muffins the same day they’re baked. Thaw at room temperature before serving.