Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper. In a medium bowl, whisk together flour, baking soda, salt, and cinnamon (if using) then set aside. In a large mixing bowl whisk the melted butter and brown sugar until smooth, add the eggs and vanilla extract and mix until fully combined, stir in the sour cream (or yogurt), then add the mashed bananas.

Add the dry ingredients to the wet mixture. Gently fold the batter together using a spatula or spoon. Do not overmix—stop when just combined. Fold in nuts or chocolate chips if using. Pour the batter into the prepared loaf pan. Bake for 50–60 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.

Let the banana bread cool in the pan for about 10–15 minutes, then transfer it to a wire rack to cool completely before slicing.