Preheat your oven to 325°F (163°C) and prepare an 8x5 inch loaf pan by greasing it or lining it with parchment paper.

In a medium bowl, whisk together the flour, baking soda, salt, and cinnamon until well combined.

In a separate bowl, whisk the egg with granulated sugar and vegetable oil until smooth.

Slowly add the dry mixture to the wet ingredients and mix gently until just incorporated.

Fold in the buttermilk, vanilla extract, and mashed ripe bananas until you have a slightly lumpy batter.

Pour the batter into the prepared loaf pan and sprinkle walnuts on top if desired.

Bake the banana bread in the preheated oven for 60 to 75 minutes, checking for doneness with a toothpick.

Let the banana bread cool in the pan for about 10 minutes, then turn it out onto a wire rack to cool completely.