Lay two slices of bread on a clean flat surface. Spoon 2 tablespoons of Nutella onto the center of each slice, spreading it gently but keeping a 1.5 cm (½ inch) clear border around all edges.
Place the remaining two bread slices on top of the filled slices. Press the edges firmly together with your fingertips, then use a fork to crimp all the way around the border to create a tight, secure seal.
Brush melted butter generously over both sides of each assembled pie, making sure every area is coated evenly.
Preheat your air fryer to 180°C (360°F) for 3 minutes. Place the pies flat in the basket without overlapping. Air fry for 5 to 6 minutes, flipping once at the halfway point, until both sides are deep golden brown.
Remove the pies carefully and let them rest on a plate or wire rack for 2 minutes before serving. Dust with powdered sugar and slice diagonally to serve.
Notes
Do not skip the resting time — the Nutella filling reaches very high temperatures inside. The 2-minute rest prevents burns and lets the filling settle to the perfect gooey consistency. For extra crunch, sprinkle a tiny pinch of flaky sea salt over the powdered sugar before serving.