Preheat oven to 350F and grease a silicone muffin pan (I haven’t tried regular muffin pans so if you’re using one or even muffin liners make sure to grease well).
In a food processor, hand mixer or by hand blend together mashed banana, egg, yogurt, nutella, vanilla extract until smooth.
In a medium bowl whisk together flour, cocoa powder, salt, baking soda, baking powder.
Pour in the wet ingredients and fold until combined (do not overmix).
Fill 9 muffin cavities 1/3 of the way.
Drop a heaping tsp of nutella on each (about 8 g per muffin) and top with the rest of the batter until they’re 2/3 full.
Bake for 20-25 minutes.
Let cool in the muffin pan a few minutes then transfer to a wire rack. Enjoy!