Step 1: In a large bowl, mash the ripe bananas until smooth, leaving a few small lumps for texture if desired.
Step 2: Add the melted butter (or vegetable oil), brown sugar, white sugar, eggs, and vanilla extract (if using) to the mashed bananas. Whisk until the mixture is smooth and well combined.
Step 3: In a separate bowl, combine the all-purpose flour, baking soda, baking powder, salt, and nutmeg (if using). Whisk well to ensure all dry ingredients are evenly distributed.
Step 4: Gently fold the dry ingredient mixture into the wet banana mixture until just combined. Be careful not to overmix, as this can lead to a tough loaf. A few streaks of flour are acceptable.
Step 5: Pour the batter into a greased 9x5-inch loaf pan. Bake in a preheated oven at 175°C (350°F) for 50–60 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Step 6: Let the banana bread cool in the loaf pan on a wire rack for 10–15 minutes before carefully removing it from the pan. Transfer to the wire rack to cool completely before slicing and serving for the best texture.