Preheat the oven to 400°F. Line a large cookie sheet with parchment paper.
Rinse the cranberries and discard any bad ones.
Mix the chopped turkey into the gravy.
If you're using store-bought puff pastry, cut each sheet into 4 equal squares. If you're using homemade pastry, roll it out to ⅛ inch thick, then cut out six 6 ½ inch circles from the pastry. Stack the scraps and re-roll them as needed.
To assemble each pasty, place a spoonful of the turkey/gravy mixture in the middle of the pastry. Add 4-5 sweet potato cubes, 3-4 cranberries, and a sprinkle of onion and garlic on top. Be careful not to overfill.
Brush half of the pastry edge with beaten egg, then fold over the top. Press the seam together gently and crimp with a fork to seal. Transfer to the prepared cookie sheet, and repeat step 5 with the remaining pastry.
Brush all of the pasties with beaten egg, poke two vent holes in each one, and chill for 10 minutes in the fridge.
Bake at 400°F for 25-30 minutes, until the pastry has puffed and is a rich golden brown.
Transfer the pasties to a wire rack and let them cool for 20-30 minutes before eating. Enjoy while fresh and warm!