Preheat your oven to 350°F. Grease a mini loaf pan, line with parchment paper sling (optional), and set aside.
In a medium bowl, whisk together sugar, flour, nutmeg, baking powder, baking soda, and salt.
In a separate medium bowl, mash the banana and whisk in the egg until well-combined. Pour banana mixture into the dry ingredients and mix until just-combined.
Add melted butter, and mix until butter is incorporated into the batter. Don’t over mix, but there should not be pools of butter remaining around the edges of the batter.
Transfer the batter to your prepared loaf pan, leaving ¾ inch of space from the top of the pan (discard extra batter if there is too much).