Start by placing your puff pastry into the air fryer basket. It is much easier to assemble. The size of the galette is going to be dependent on what size air fryer you own.
In a small mixing bowl, add the blueberries, sugar, lemon juice, and cornstarch, and mix well.
Place the blueberries in the center. The amount is going to be determined by how big your galette is. The large gallate will use all the fillings; if you have a smaller air fryer, you must do 3 galettes, so divide the filling accordingly.
Fold the edges up and over the edge of the pastry, and do it all around. Press the dough together.
In a small bowl, crack the egg and mix in 1 tablespoon of water; this is your egg wash.
Use a pastry brush and brush the pastry with egg wash. Then sprinkle some of the sparkling sugar over the pastry.
Set in the air fryer at 330 degrees F for about 15-20 minutes.
Plate, serve, and enjoy!