Preheat oven to 175°C (350°F). Grease and flour a 9×5-inch loaf pan or line with parchment paper.
In a large bowl, whisk together the flour, baking soda, salt, and cinnamon.
In a separate medium bowl, mash the bananas. Add the oil, brown sugar, granulated sugar, eggs, vanilla, and sour cream. Whisk until well combined.
Pour the wet mixture into the dry ingredients. Using a spatula, fold gently until just combined. Do not overmix; a few streaks of flour are okay.
If using, fold in 1 cup of chocolate chips or chopped nuts.
Pour the batter into the prepared pan and smooth the top.
Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean. If the top is browning too quickly, tent with foil for the last 15-20 minutes.
Let the bread cool in the pan for 15 minutes before transferring to a wire rack to cool completely before slicing.