Peel celery root and place in a saucepan. Cover with water and boil until tender, about 20 to 25 minutes. Remove and pass through vegetable mill and allow to cool. Place in a mixing bowl with cream, yolks, eggs and 2 tablespoons of Parmesan cheese and stir well to blend. Season with salt and nutmeg and pour into 6 4-inch tall flan molds. Place flan molds in a gratin dish and fill halfway with cool water. Place in oven and bake until set, about 30 to 40 minutes. Remove and allow to cool slightly. Meanwhile, heat oil in a 12 inch saute pan over medium heat. Add leeks and garlic and cook until quite soft, about 9 to 10 minutes. Add muscat and bring to a boil and reduce until 4 tablespoons remain. Add butter and swirl to emulsify and remove from heat. Unmold flans and place upside down on plates. Spoon warm leek mixture over and sprinkle with remaining cheese.
