Preheat your oven to 400°F (200°C).

Spray a muffin tin with nonstick cooking spray.

Roll out the thawed puff pastry sheets on a floured surface and cut into squares (about 4 inches).

Gently press each square into the muffin tin cups, leaving some overhang.

Spread about 1 tablespoon of Nutella in each cup and layer sliced bananas on top.

Whisk together the egg and water, then brush the mixture over the exposed pastry edges.

Bake for 15-20 minutes until golden brown and puffy.

Allow to cool slightly before dusting with powdered sugar and serving warm.