Preheat the oven to 350°F.
Grease a 9 x 5-inch loaf pan and line it with parchment paper, leaving a little overhang for easy removal.
Add the mashed bananas, dark brown sugar, and white sugar to a large mixing bowl. Whisk until combined.
Pour in the melted butter and mix well.
Add the eggs, vanilla extract, and sour cream. Whisk until smooth and fully combined.
In a separate bowl, whisk together the flour, baking powder, and salt.
Add the dry ingredients to the banana mixture and gently fold until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top.
Sprinkle the top generously with chopped pecans and chocolate chips.
Bake for 55–65 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean or with a few moist crumbs.
If the top begins browning too quickly, loosely cover the loaf with aluminum foil during the final 15–20 minutes of baking.
Allow the banana bread to cool in the pan for about 15 minutes, then lift it out and transfer it to a cooling rack.
Let cool for at least 30 minutes before slicing.