Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners or grease the cups with non-stick cooking spray.

In a large mixing bowl, whisk together the flour, granulated sugar, brown sugar, baking powder, baking soda, and salt.

In another bowl, mix the mashed bananas, buttermilk, vegetable oil, egg, and vanilla extract until well combined.

Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to overmix – a few lumps are totally fine!

Fold in the chopped pecans, reserving a handful to sprinkle on top of the muffins.

Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full. Sprinkle the reserved pecans on top of the muffins.

Bake for 20-25 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Remove from the oven and let the muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.