Preheat the oven to 425 degrees F. Prepare a muffin pan with cooking spray or paper muffin cups and get out of all the necessary ingredients.
In a medium mixing bowl, combine 3 large (about 300g or 1 cup) extra ripe bananas with 1 large egg, 1/4 cup (60ml) maple syrup or honey, 1 tablespoon oil* and 1 teaspoon pure vanilla extract. Stir vigorously until the mixture is smooth.
In a separate large mixing bowl, combine the dry ingredients; 1 cup (120g) all-purpose flour or whole wheat pastry flour, 1/2 cup protein powder, 1 teaspoon baking powder, 1 teaspoon baking soda, 1/2 teaspoon salt, 2 teaspoons ground cinnamon, 1/4 teaspoon ground nutmeg and 1 tablespoon cornstarch . For best results, spoon flour into cup (rather than scooping with cup) and then level using a butter knife. If adding in additional mix-in, such as 1/2 to 1 cup chocolate chips or chopped nuts, toss in the flour mixture.
Make a well in the center of the flour mixture and add wet ingredients. Gently stir until just combined. Don't over-mix, some small streaks of flour are fine.
Spoon batter into the prepared muffin tins filling each one completely full and top with a few additional chocolate chips, if desired. Bake muffins for 5 minutes at 425 degrees F. and then with muffins staying in the oven, reduce heat to 350 degrees F. and bake muffins for 12-15 minutes more. The high heat will cause muffins to rise and then you will lower heat to cook the center of the muffin. I recommend checking muffins after about 12 minutes because mine were completely baked by 13 minutes.
Remove from oven and allow muffins to cool in the pan for 10 minutes before transferring to a wire rack to cool completely. You might need to run a butter knife along the outer edge of the muffins to loosen them from the pan.