Preheat oven to 425 degrees. Line 18 muffin cups with paper liners, set aside.
In a large bowl, whisk together the banana, oil, butter, white sugar, brown sugar, eggs, milk (or sour cream), vanilla and bananas.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon and salt. Set aside.
Add the dry ingredients to the wet ingredients, gently fold everything together, along with 1 cup of nuts. Let the batter rest for 20 minutes.
Fill liners about 1/8-inch below the rim. They should be VERY full. Sprinkle tops with remaining nuts.
Bake for 7 minutes at 425. Reduce the heat to 375 and continue baking for another 12 minutes or until a toothpick inserted into the center comes out clean.
Let cool in pans for 5 minutes before transferring to a wire rack to cool completely. Store at room temperature for up to 3 days.