Mix together the blueberries, sugar, lemon juice, and salt in a medium bowl.
Roll out the piecrusts (or shortcrust pastry roll) and cut out 6-8 (4-inch) individual circles.
Place about 1 tablespoon of the blueberry filling in the center of each circle.
Moisten edges of dough with water, and fold the dough over the filling to form a half moon shape.
Using a fork, gently crimp the edges of the piecrust together. Then cut three slits on the top of the hand pies.
Spray the hand pies with cooking spray and sprinkle with vanilla sugar (if using).
Preheat the air fryer to 350F / 180C.
Place 3-4 hand pies in single layer inside the air fryer basket.
Cook for 9-12 mins, or until golden brown.
Let the pies cool for at least 10 mins before serving.