Make the pie filling
Preheat the oven to 200°C (400°F). In a large pan, melt the butter over medium heat until sizzling. Add the diced onion, celery, and carrots, sautéing gently until softened.
Stir in the chopped bacon or ham, Dijon mustard, and garlic paste, allowing the flavors to meld for a couple of minutes.
Sprinkle in the salt, black pepper, and dried herbs, followed by the flour or xanthan gum. Stir well to coat the ingredients evenly.
Pour in the hot chicken stock (or leftover gravy) along with the cream, stirring continuously as the sauce thickens.
Fold in the chopped dried cranberries, grated Parmesan, and shredded turkey, ensuring everything is well coated in the rich sauce.
Add the topping and bake
Transfer the mixture into a ceramic or pie dish, spreading it evenly.
Cut the puff pastry into decorative shapes, such as stars, and layer them over the filling, slightly overlapping. Alternatively, use a whole sheet of puff pastry, ensuring to score the top to allow steam to escape. Brush with beaten egg.
Sprinkle with grated Parmesan and a pinch of nutmeg for extra depth of flavor.
Place the dish on a baking tray to catch any spills, then bake for 30–35 minutes, or until the pastry is golden brown and the filling is bubbling.
Allow to cool slightly before serving with a crisp salad or steamed greens.