Preheat oven to 400°F/ 200°C. Grease 16 regular muffin cups, and set aside.

In a large bowl, mix together the flour, sugar, baking powder, baking soda, and half the amount of chopped pecans.

In a separate bowl, whisk together the buttermilk, mashed bananas, oil, egg, and vanilla.

Pour wet ingredients over dry ingredients and stir just until blended.

Spoon batter into muffin cups, filling about three-fourths full.

Sprinkle tops evenly with remaining chopped pecans.

Bake for 15-20 minutes or until muffin tops are lightly brown and a toothpick inserted in center comes out clean.

Allow to cool in pan on wire rack for 15 minutes, then turn out onto rack and cool completely.