Preheat oven to 375°F. Prepare two mini muffin tins with paper liners (or just use same muffin tin twice) or grease with butter or nonstick cooking spray.
In a medium sized bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
Put bananas in a separate large bowl and mash them really well with a fork.Add in melted butter, oil, buttermilk, eggs, and vanilla, mix well. Next, add in brown sugar and white sugar, combine well.
Add dry ingredients into wet ingredients, mixing until just combined. Making sure not to over-mix.
Spoon batter into muffin tin, filling each about 2/3 of the way full.
Place one muffin tray on center rack in the oven and bake for 12-15 minutes. Check muffins for doneness by inserting a toothpick into the center of one of the bigger muffins. It should come out with a few crumbs, but no uncooked batter. Move all muffins onto a cooling rack.
Either place second muffin tray into the oven or fill the same muffin tray with muffin and place that into the oven. Cook for 12-15 minutes, check for doneness.
Let muffins cool before eating.