Preheat your oven to 350F (175C) and line a 12-count cupcake tin with paper liners. Set aside.
Make sure bananas are very well mashed (I often start with a fork or potato masher and then switch over to my mixer) then add melted butter, oil, and sugars and stir very well to combine.
Add eggs and vanilla extract and stir well, then stir in buttermilk.
In a separate bowl, whisk together flour, baking powder, baking soda, and salt.
Add dry ingredients to batter and use a spatula to gently fold together until combined. Batter should be completely combined, but don’t over-mix or your cupcakes may be dense and dry!
Portion batter into cupcake liners, filling each ¾ full. If you have extra batter, discard or make additional cupcakes.
Transfer to 350F (175C) oven and bake for 17-18 minutes or until a toothpick inserted in the center comes out clean or with a few moist crumbs. Allow to cool completely before frosting with my brown butter frosting (or see other options in my notes).