Preheat oven to 350°F. Butter a 9×5-inch loaf pan; set aside. In a large bowl, whisk together the flour, cinnamon, baking powder, baking soda, salt, and nutmeg. In a separate bowl, whisk together the 1/2 cup melted butter, the bananas, sugar, and eggs. Stir in the vanilla. Stir the banana mixture into the flour mixture until just combined.