Step 1: Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter or cooking spray and line with parchment paper.
Step 2: In a large mixing bowl, mash the overripe bananas until mostly smooth with a few small chunks remaining.
Step 3: Add the vegetable oil, eggs, vanilla extract, and sour cream to the mashed bananas. Whisk together until well combined and slightly frothy.
Step 4: Stir in both the granulated sugar and brown sugar until dissolved. Let the mixture sit for 2-3 minutes.
Step 5: In a separate bowl, whisk together the flour, baking soda, salt, and cinnamon until evenly distributed.
Step 6: Add the dry ingredients to the wet mixture in two additions, folding gently with a spatula until just combined. A few flour streaks should remain visible. Do not overmix.
Step 7: Pour the batter into the prepared loaf pan, spreading evenly. Gently tap the pan on the counter to release air bubbles.
Step 8: Bake for 60-70 minutes, or until a toothpick inserted into the center comes out with just a few moist crumbs. The internal temperature should reach 200-205°F.
Step 9: Remove from oven and let the bread rest in the pan for 15 minutes.
Step 10: Transfer the loaf to a wire rack and let cool for another 30-45 minutes before slicing and serving.
