Preheat your oven to 325°F (163°C). Spray an 8x5 inch loaf pan with nonstick spray to prevent sticking. If you like, line it with parchment paper for easier removal after baking.

In a medium bowl, combine the all-purpose flour, baking soda, salt, and ground cinnamon. Whisk these ingredients together just until evenly distributed and combined. This ensures the leavening and spices are well mixed throughout the loaf for even flavor.

In another medium bowl, whisk together the egg, granulated sugar, and vegetable oil until the mixture is uniform. The sugar will start to dissolve, creating a smooth base for the batter.

Add the dry ingredients from Step 2 into the wet ingredients from Step 3. Mix well until everything is just combined; the mixture will look thick and a bit dry at this point. Now, add the buttermilk, vanilla extract, and mashed bananas. Stir until a cohesive, slightly lumpy batter forms, being careful not to overmix. Personally, I like to leave some small banana lumps for extra flavor bursts in each bite.

Pour the banana bread batter into the prepared loaf pan from Step 1, spreading it out evenly. Sprinkle the chopped walnuts evenly over the top. The nuts will toast as the bread bakes, adding extra crunch and flavor.

Place the loaf pan on the center rack of your preheated oven. Bake for 60 to 75 minutes, or until a knife or skewer inserted into the center comes out clean. If the top is browning too quickly, you can loosely tent the bread with foil during the last 15-20 minutes. Let cool before slicing and serving—this helps set the texture for perfect slices.