Paris-based chef Daniel Rose gives his vegetable gratin maximum flavor by adding rich duck confit (instead of bacon or sausage). Slideshow: More Celery Root Recipes
In a small bowl, combine the raisins with water to cover by 2 inches and let stand for 1 hour. Drain.
Meanwhile, preheat the oven to 425°. Brush a 3-quart shallow baking dish with butter.
In a large saucepan of salted boiling water, cook the celery root until tender, about 15 minutes. Drain well. In a food processor, puree half of the celery with the cream, egg yolk and 2 tablespoons of the butter until smooth. Season with salt and pepper. Scrape the mixture into a large bowl and stir in the remaining celery root.
In a large skillet, melt the remaining 2 tablespoons of butter. Add the pears and cook over moderately high heat, stirring occasionally, until golden, about 3 minutes. Fold into the celery root.
In a medium bowl, combine the duck confit with the orange zest, cinnamon and 3 tablespoons of the raisins. Spread the duck in the prepared dish and spoon the celery root mixture evenly over it. Bake for about 15 minutes, until heated through; remove the dish from the oven. Position a rack in the oven 8 inches from the heat and preheat the broiler on high. Broil the gratin for about 5 minutes, until golden. Top with the remaining 1 tablespoon of raisins and serve warm.