Unroll crescent dough and separate into triangles or cut puff pastry into 3-inch squares.
Slightly flatten each piece of dough.
Place about 1 tablespoon Nutella in the center of each dough piece.
Fold dough around the Nutella and pinch edges tightly to seal, then roll gently into smooth balls.
Brush each ball lightly with beaten egg for a golden finish.
Preheat air fryer to 350°F (175°C).
Arrange balls in the air fryer basket, leaving space between each.
Air fry balls for 7 to 9 minutes until puffed and golden brown.
Brush warm balls with melted butter.
Mix granulated sugar and cinnamon in a small bowl.
Roll or sprinkle the Nutella Balls in the cinnamon sugar coating.