Preheat your oven to 350°F (175°C) and grease or line a 9x13-inch baking pan with parchment paper.

In a large mixing bowl, mash 2-3 overripe bananas until smooth.

Combine the mashed bananas with the sugars, melted butter, eggs, sour cream, and vanilla extract, whisking until smooth.

In a separate bowl, whisk together the flour, baking soda, and salt.

Gently fold the dry mixture into the wet banana mixture until just combined.

If desired, fold in chopped walnuts or mini chocolate chips.

Spread the batter evenly into the prepared baking pan and bake for 25-30 minutes.

Allow the brownies to cool in the pan for 10-15 minutes before transferring to a wire rack to cool completely.

Once cooled, slice the brownies into squares for serving.