Preheat the oven to 350°F. Grease or spray a 9×5-inch loaf pan.
In a large bowl, mash the bananas with a fork until mostly smooth, leaving a few small lumps.
Stir in the melted, slightly cooled butter, egg, sugar, vanilla extract, and sour cream until well combined. Add the baking soda and salt and stir to combine.
Add the flour and gently stir just until no dry streaks remain. Do not over mix.
Fold in the chocolate chips.
Pour the batter into the prepared loaf pan and spread it into an even layer.
Bake for 50–60 minutes, checking at the 50-minute mark. The bread is done when a toothpick inserted into the center comes out with a few moist crumbs (not wet batter).
Let the bread cool in the pan for 10–15 minutes, then carefully transfer it to a wire rack to cool completely before slicing.
Notes
Use bananas that are heavily speckled or mostly black for the best flavor and moisture.If the top starts browning too quickly, loosely cover it with aluminum foil during the last 15–20 minutes of baking.Store tightly wrapped at room temperature for up to 3 days, or refrigerate for up to a week. It also freezes well for up to 3 months.