Prep oven and filling: Preheat oven to 400°F. In a pot, melt butter over medium heat. Add apples and cook 5 minutes.
1 ¼ pounds Granny Smith apples, 1 tablespoon unsalted butter, ¼ cup brown sugar, ½ teaspoon ground cinnamon, ⅛ teaspoon salt
Add flavor: Stir in brown sugar, cinnamon, and salt. Simmer on low 3 minutes until apples are soft and caramelized. Let cool.
Roll and cut pastry: Roll out one sheet of puff pastry into an 11" square. Cut into 4 squares using a pizza cutter.
1 pounds puff pastry, 1 tablespoon all-purpose flour
Fill and fold: Spoon apple mixture onto half of each square, leaving a ½-inch border. Brush edges with egg wash. Fold into triangles and crimp with a fork to seal.
1 egg+ 1 tablespoon water for egg wash
Chill and prep: Place assembled turnovers on a parchment-lined baking sheet. Chill in the fridge for 15–20 minutes.
Bake: Cut small slits in the top of each turnover. Brush tops with egg wash and bake 20–22 minutes, until puffed and golden.
Glaze: While warm, whisk powdered sugar with cream or lemon juice and drizzle over turnovers.
½ cup powdered sugar, 1-2 tablespoon lemon juice