Step 1: Preheat and Prepare
Preheat your oven to 350°F (175°C). Grease a 9×5-inch loaf pan generously with butter or non-stick spray, or line it with parchment paper, leaving overhang on the sides for easy removal. Set aside.

Step 2: Toast the Walnuts
While the oven preheats, place chopped walnuts in a dry skillet over medium heat. Toast for 3-5 minutes, stirring frequently, until fragrant and lightly golden. Watch carefully as they can burn quickly. Remove from heat and set aside to cool. This step is optional but highly recommended for maximum flavor.

Step 3: Mash the Bananas
Peel the overripe bananas and place them in a large mixing bowl. Using a fork or potato masher, mash until mostly smooth with just a few small lumps remaining. You should have about 1½ cups of mashed banana. A few small chunks are fine and actually add nice texture.

Step 4: Mix Wet Ingredients
Add the melted butter to the mashed bananas and stir until combined. Add the sugar and mix well until the mixture looks smooth and slightly glossy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and sour cream if using. Mix until everything is well combined and smooth.

Step 5: Add Dry Ingredients
In a small bowl, whisk together the flour, baking soda, salt, and cinnamon if using. Add the dry ingredients to the wet ingredients all at once. Using a wooden spoon or rubber spatula, gently fold the dry ingredients into the wet ingredients just until no white streaks of flour remain. Be careful not to overmix – the batter should look thick and somewhat lumpy. Overmixing develops gluten and creates tough, dense bread.

Step 6: Fold in Walnuts
Gently fold in the toasted walnuts, reserving a small handful to sprinkle on top if desired. The batter will be thick – this is normal and exactly what you want.

Step 7: Transfer to Pan
Pour the batter into the prepared loaf pan and spread it evenly with a spatula. Tap the pan gently on the counter a couple times to remove any air bubbles. If desired, sprinkle the reserved walnuts on top and gently press them into the batter.

Step 8: Bake
Bake in the preheated oven for 60-65 minutes. The bread is done when the top is deeply golden brown, a toothpick inserted into the center comes out clean or with just a few moist crumbs (not wet batter), and the internal temperature reaches 200-205°F. If the top is browning too quickly after 45 minutes, tent loosely with aluminum foil for the remaining baking time.

Step 9: Cool and Serve
Remove from the oven and let the bread cool in the pan on a wire rack for 10-15 minutes. This cooling period is crucial – it allows the bread to set and makes it easier to remove from the pan. After 15 minutes, carefully remove the bread from the pan (use the parchment overhang if you used it) and let it cool completely on the wire rack before slicing, about 30-45 minutes. For the cleanest slices, wait until completely cool, though warm banana bread is absolutely irresistible!