In a medium bowl, combine flour, baking soda, and baking powder.
In a large mixing bowl, beat butter and sugar until combined.
Add sour cream, vanilla, and eggs, beating until combined.
Fold in bananas.
Line 18 regular-sized muffin cups with paper liners.
Fill the cups 3/4-full with cupcake batter - these don't rise a lot.
Bake at 350 degrees for 18-22 minutes, or until edges are golden brown.
Remove to wire racks to cool completely.
To fill: Using a small spoon or small cookie scoop, carefully scoop a 1-inch ball of cake out of the top of each cupcake.
Fill the divot with about 1-inch rounded scoop of Nutella. I used the entire jar.
You can replace the cake ball on top of the Nutella, or not! I sometimes frost right over the filling, without replacing it, but you can add the tops back onto the cupcakes if you'd like.