Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and line a 9×5-inch loaf pan with parchment paper or butter to prevent sticking.

Mash the Bananas: In a large bowl, mash the ripe bananas with a fork or potato masher until smooth, leaving a few chunks for texture if preferred.

Combine Butter and Sugars: In a separate bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy (about 2-3 minutes using a hand mixer).

Add Eggs and Sour Cream: Beat in the eggs one at a time, ensuring each is well incorporated. Add sour cream and vanilla extract, mixing until smooth.

Add the Bananas: Stir the mashed bananas into the butter and sugar mixture until fully combined.

Add Dry Ingredients: In another bowl, whisk together the all-purpose flour and baking soda. Gradually add the dry ingredients to the wet mixture, stirring gently until just combined (do not overmix).

Fold in Walnuts: If using, gently fold the walnuts into the batter.

Bake: Pour the batter into the prepared loaf pan and smooth the top. Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.

Cool: Allow the banana bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely. This helps maintain its shape and makes it easier to slice.