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

In a large mixing bowl, combine the mashed bananas and sugar. Mix until well combined.

Add the softened butter to the banana mixture and stir until creamy.

Beat in the eggs, one at a time, followed by the vanilla extract and sour cream. Mix until smooth.

In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon (if using).

Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Be careful not to overmix.

If desired, fold in the chopped nuts.

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 before transferring it to a wire rack to cool completely.