Preheat your oven to 425°F (218°C). Line a 12-cup muffin tin with paper liners or spray with non-stick cooking spray. Set aside.
In a medium bowl, sift together the flour, baking soda, and salt. Set aside.
1 ½ cups all-purpose flour, 1 teaspoon baking soda, 1 teaspoon kosher salt
In a large mixing bowl, use an electric mixer to cream the butter, sugar, and eggs until light and fluffy.
½ cup unsalted butter, 1 cup granulated sugar, 2 large eggs
Mash the bananas and add them to the butter mixture along with the sour cream and vanilla extract. Mix until well combined.
1 cup mashed overripe bananas, ½ cup sour cream, 1 teaspoon vanilla extract
Add the flour mixture to the wet ingredients, mixing until just combined. Do not overmix.
Using an ice cream scoop or measuring cup, fill each muffin cup about ⅔ full with batter.
Bake at 425°F for 5 minutes. Then, without opening the oven door, reduce the oven temperature to 350°F (175°C) and continue baking for an additional 16-18 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Allow the muffins to cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely.