Preheat the oven to 375 degrees. Prepare a 6 cup jumbo muffin pan with jumbo baking liners spritzed with nonstick cooking spray.
In a small bowl mashed the bananas with a fork. Set aside.
In a small bowl, stir together the flour, baking soda, baking powder, and salt. Set aside.
In a mixing bowl, beat the butter until creamy, about 5 minutes. Add the sugar, scraping down the sides, until the butter and sugar are completely blended and fluffy. Mix in the eggs, buttermilk, mashed bananas, and vanilla.
To the liquid mixture, add the dry ingredients and stir just until blended. Add the pecans and fold to mix into the batter.
Divide the batter between the 6 muffin cups. Sprinkle additional pecans on top for decoration if desired.
Bake the muffins for 25 to 30 minutes or until a toothpick inserted in the middle returns clean.
Cool for 5 minutes in the muffin pan on a wire rack before removing the muffins from the pan. Serve the muffins while warm.