In a medium saucepan, combine the 1 1/2 cups Blueberries, 1/4 cup Granulated Sugar, and 1 teaspoon Lemon Zest.
Cook over medium heat until the blueberries start to release their juices, stirring occasionally.
Make a slurry by mixing 1 tablespoon Cornstarch and 1 tablespoon Water in a separate bowl until smooth.
Slowly add the slurry to the blueberry mixture, stirring constantly until the mixture thickens.
Remove from heat and let it cool.
Lay out the thawed 2 sheets Puff Pastry on a lightly floured surface. Using a knife or pizza cutter, cut each sheet into squares or rectangles, depending on your preference.
Spoon a generous amount of the blueberry filling into the center of each pastry square.
Fold the pastry over the filling to form a triangle (or rectangle, depending on your initial cut). Press the edges to seal. You can also use a fork to crimp the edges and ensure a tight seal.
Beat the 1 large Egg and brush it over the tops of the turnovers to give them a glossy finish when they cook.
Preheat your air fryer to 375°F (190°C), for 3-5 minutes.
Place the turnovers in the air fryer basket in a single layer.
Air fry for 8-10 minutes or until the turnovers are golden brown and puffed up.
Once cooked, remove the turnovers from the air fryer and let them cool slightly on a wire rack. Dust with 1/4 cup Powdered Sugar