Step 1: Preheat your oven to 350°F (175°C). Grease and flour a 9x5 inch loaf pan, or line with parchment paper leaving an overhang.
Step 2: In a large bowl, mash the very ripe bananas with a fork or potato masher until mostly smooth with a few small lumps remaining.
Step 3: In a separate medium bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined. Beat in the room temperature egg and vanilla extract until smooth.
Step 4: Add the wet sugar mixture to the mashed bananas and stir until just combined.
Step 5: In another bowl, whisk together the all-purpose flour, baking soda, and salt.
Step 6: Gradually add the dry ingredients to the wet ingredients, mixing with a spoon or spatula until just combined. Be careful not to overmix; a few lumps are fine.
Step 7: If using, gently fold in the chocolate chips or chopped walnuts.
Step 8: Pour the batter evenly into the prepared loaf pan.
Step 9: Bake for 55-65 minutes, or until a wooden skewer or toothpick inserted into the center comes out clean or with a few moist crumbs attached.
Step 10: Let the banana bread cool in the loaf pan for 10-15 minutes before carefully transferring it to a wire rack to cool completely. Slice and serve.