Preheat the Oven:
Set oven to 350°F (175°C) and grease or line a 9x5-inch loaf pan with parchment paper.
Mash the Bananas:
In a large bowl, mash bananas until smooth but still slightly chunky for texture.
Mix Wet Ingredients:
Stir in melted butter, brown sugar, eggs, and vanilla extract. Mix until smooth and well blended.
Combine Dry Ingredients:
In another bowl, whisk flour, baking soda, salt, and cinnamon.
Mix Together:
Gently fold the dry ingredients into the wet mixture until just combined. Add sour cream or yogurt and mix lightly.
Add Optional Mix-Ins:
Fold in nuts or chocolate chips if using.
Bake:
Pour the batter into your prepared loaf pan. Bake for 55–65 minutes, or until a toothpick inserted in the center comes out clean.
Cool and Serve:
Let your banana loaf cool in the pan for 10 minutes before transferring to a rack to cool completely. Slice and enjoy warm or at room temperature.