- Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper for easy removal. 
- In a large mixing bowl, combine the mashed bananas and peanut butter until smooth. 
- Add the granulated sugar, brown sugar, eggs, and vanilla extract to the banana mixture. Mix well until fully combined. 
- In a separate bowl, whisk together the baking soda, salt, and flour. Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Do not overmix. 
- If using, fold in the chopped walnuts. 
- Pour the batter into the prepared loaf pan and smooth the top with a spatula. 
- Bake in the preheated oven for 55-65 minutes, or until a toothpick inserted into the center comes out clean. 
- Allow the bread to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.