Preheat oven to 350°F (177°C). Grease 9×5-inch loaf pan and line with parchment paper overhanging sides for easy removal. Mash peeled overripe bananas in medium bowl using fork until mostly smooth with small chunks. Set aside. In large bowl, beat softened butter with granulated sugar and brown sugar 4-5 minutes until light, fluffy, and pale (or vigorously stir if using melted butter for no-mixer version). Add eggs one at a time, beating well after each. Mix in vanilla extract and mashed bananas. Scrape down bowl sides. In separate bowl, whisk together flour (spooned and leveled), baking powder, baking soda, cinnamon, and salt. Gently fold dry ingredients into wet batter until just combined (no flour streaks visible). Do not overmix. Fold in walnuts or chocolate chips if using. Pour batter into prepared pan and smooth top evenly. Bake 55-65 minutes, tenting with foil after 45 minutes if browning too quickly. Toothpick inserted in center should come out clean or with a few moist crumbs. Cool in pan 20 minutes, then lift using parchment and transfer to wire rack to cool completely before slicing.