Preheat the oven to 350°F. Grease an 8½ x 4½ inch loaf pan and lightly flour it or line with parchment for easy removal.

In a medium bowl, whisk the flour, baking soda, and salt until evenly combined. Set aside.

In a large bowl, mash the ripe bananas with a fork until mostly smooth. Add the sugar, eggs, melted butter, sour cream, and vanilla. Whisk until the mixture is uniform.

Pour the dry mixture into the wet ingredients. Fold gently with a spatula until just combined; a few streaks of flour are okay. Overmixing will make the loaf tough.

Transfer the batter to the prepared pan and smooth the top with a spatula so it bakes evenly.

Bake on the middle rack for 50 to 60 minutes. Check at 50 minutes by inserting a toothpick in the center; it should come out clean or with a few moist crumbs. If the top browns too quickly, tent loosely with foil.

Let the loaf cool in the pan for 15 minutes, then lift out and finish cooling on a rack before slicing to keep slices neat.