Make the custard by whisking together milk, heavy cream, egg, and vanilla extract. Set aside.

Trim crusts from bread slices and flatten them with a rolling pin.

Spread Nutella on each bread slice and roll them up, pinching seams to secure.

Heat 2 tablespoons of butter in a skillet over medium heat. Dip rolls in custard and cook until golden, flipping to cook all sides.

Roll cooked rolls in vanilla sugar or dust with powdered sugar and serve immediately.