Step 1: Preheat Oven : Preheat oven to 350°F (175°C). Grease a 9x5-inch loaf pan or line it with parchment paper.

Step 2: Mix Dry Ingredients : In a medium bowl, whisk together flour, baking soda, salt, and cinnamon (if using).

Step 3: Cream Butter and Sugar : In a large bowl, cream together the softened butter and sugar until light and fluffy.

Step 4: Add Wet Ingredients : Beat in eggs, one at a time, followed by vanilla extract. Mix in mashed bananas and sour cream until combined.

Step 5: Combine Wet and Dry Ingredients : Gradually fold the dry ingredients into the wet mixture until just combined. Do not overmix.

Step 6: Add Chocolate Chips and Walnuts : Gently fold in chocolate chips and chopped walnuts, reserving a few for topping if desired.

Step 7: Bake : Pour the batter into the prepared loaf pan. Sprinkle reserved chocolate chips and walnuts on top. Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.

Step 8: Cool : Allow the banana bread to cool in the pan for 10-15 minutes, then transfer to a wire rack to cool completely before slicing.