Preheat oven to 425.
Line muffin pan with paper or silicone liners.
Mash bananas in medium bowl until no, or very few. lumps remain.
Add oil and melted butter, mix well.
Add sugars, mix until combined.
Add eggs, vanilla extract, and buttermilk, mix well. Set aside.
In a separate bowl, whisk together flour, baking powder, and baking soda.
Add dry ingredients to wet ingredients and fold together until just combined. Do not over mix.
Pour batter into prepared tins, about 3/4 full. I usually make about 16-17 muffins per batch, so I use two tins.
Prepare sugar topping by adding sugar and flour to medium bowl.
Using a pastry cutter, cut in the cold butter until it resembles course crumbs.
Sprinkle topping over evenly over muffins.
Bake at 425 for 8 minutes.
Turn heat down to 350 and bake an additional 7-8 minutes. A toothpick inserted should come out clean.
Allow to cool 20 minutes. Enjoy!