NOTE: For best results, work with one puff pastry sheet at a time, leaving the second sheet in the refrigerator.
Lightly dust a clean work surface with flour. Carefully unfold 1 pastry sheet. If the pastry does not unfold easily, allow it to rest at room temperature for a few more minutes to thaw. Roll the pastry out into a 16x12-inch rectangle with the longest side facing you.
Spoon half the apple filling onto the bottom half of the pastry into 4 mounds, leaving a 1-inch border along the bottom and sides. Brush some of the reserved apple liquid around and in-between the mounds.
Pull the top half of the pastry over the bottom half, covering the filling. Pinch the edges tightly to seal. Using a pizza wheel or sharp knife, cut in between the mounds of apple filling creating 4 equal sized tarts. For each tart, pinch the edges together firmly to seal and tuck under. Place the tart on the parchment lined baking sheet, seam-sides down. Repeat with the remaining tarts.
Brush the top of the pastries with the beaten egg wash. Cut 3 or 4 slits on top of each pastry then sprinkle with almonds, pressing lightly to adhere.
Bake 18-20 minutes or until golden brown on the bottom. Remove to a wire rack to cool. While the first batch is in the oven, repeat with the second sheet of pastry and the remaining apple filling.
Serve slightly warm or at room temperature. Dust with powdered sugar just before serving.