Make the filling.In a bowl, combine Nutella and powdered sugar, then mix together until smooth. Use a 1 inch scoop to make into balls. Place balls on a cookie sheet lined with parchment paper and place in freezer. Make the cookies.In a bowl, combine bananas, vanilla, butter and brown sugar. Mix on medium speed until fully blended. Add in baking soda, salt and flour and mix on medium speed until combined. Don't over blend. Cover and place in fridge for 1-2 hours.
Preheat oven to 350 degrees.
Remove dough from the fridge and allow to get back to room temperature.
Scoop the cookie dough and flatten like a pancake. Roughly 2×2 inches. Place a frozen Nutella ball on top and fold the dough up to wrap around the frozen ball of Nutella. Make sure it's completely sealed by rolling it into a ball between your two palms. Add more cookie dough if needed to fully cover frozen ball. (This mixture is sticky so I sprayed my fingers with cookie spray to keep it from sticking).
Place granulated sugar in a small bowl, roll the stuffed cookie dough balls in the sugar and place on a cookie sheet 2 inches apart.
Bake until the cookies are golden, 12-15 minutes. Eat up and Enjoy!