Use a firm, sweet-tart apple like Honeycrisp or Cosmic Crisp — soft varieties like Fuji can turn mushy and watery in the oven. Don't stack the apple slices or the filling won't cook evenly. Scraps from cutting the pastry sheets make a great snack in the air fryer. To store, layer in an airtight container with parchment and refrigerate or freeze. Reheat in the air fryer or toaster oven — avoid the microwave.