Preheat your oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan with parchment paper for easy lifting.

In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Add the eggs and vanilla, whisking until the mixture is creamy and well blended. Stir in the mashed bananas and sour cream.

In a separate bowl, combine the flour, baking soda, baking powder, salt, cinnamon, and nutmeg. Gently fold the dry mixture into the wet ingredients, stirring only until the flour disappears. Overmixing here makes banana bread tough, so light hands are best.

Fold in the walnuts and chocolate chips if you’re using them. Scrape the batter into the prepared loaf pan and smooth the top.

Bake for 55–65 minutes, checking at the 55-minute mark. A toothpick inserted into the center should come out mostly clean, with just a few moist crumbs. Let the bread cool in the pan for 10 minutes, then lift it out and finish cooling on a wire rack.