The Thanksgiving Leftovers Croque Madame.

1. Add the gravy and milk to a small pot and bring to a gentle boil. Add a pinch of nutmeg. Remove from the heat and stir in 1 cup Gruyère and the parmesan, stirring until melted.2. Preheat the the oven to 425 degrees F. 3. Place the 4 bottom halves of the croissants on a parchment lined baking sheet. Spread 1 tablespoon mustard over each. Spoon over a layer of mashed potatoes. Drizzle the cheese sauce over the mashed potatoes. Top with turkey, cranberry sauce, any leftover vegetables, and a slice crispy prosciutto. Add the top croissant. Spoon the remaining cheese sauce over the sandwich, then top each with the remaining Gruyère. Bake until cheese sauce is bubbling and evenly browned, about 3–4 minutes.4. Meanwhile, fry the eggs. 5. Place an egg on top of each sandwich, and serve hot with a few fried sage leaves. Grab your forks and knives!