Root Vegetable Gratin with Gruyère

I got this recipe from a Williams-Sonoma catalogue around a year ago, maybe December 2007? I made it twice, and both times, friends demanded the recipe. What's not to like, with all that cream and cheese? I love celery root and love to find new ways to use it. Also this recipe allowed me to use the fancy box slicer that my step-sister-in-law sent me for Christmas last year. But I have to admit, I haven't made this recipe myself in almost a year because it's too rich even for ME, and that's saying a lot!

1 Tbsp. unsalted butter
3 garlic cloves, minced
3 cups heavy cream
Salt and freshly ground pepper, to taste
1/4 tsp. freshly grated nutmeg
1 lb. parsnips, peeled, sliced 1/8” thick
1 lb. sweet potatoes, peeled, sliced 1/8” thick
1 lb. celery root, peeled, sliced 1/8” thick
8 oz. Gruyère cheese, shredded
1 Tbsp. minced fresh thyme
3 Tbsp. minced fresh flat-leaf parsley

Preheat oven to 400 degrees. Butter a 3-quart baking dish.

In large saucepan over medium heat, melt butter. Add garlic; cook 1 minute. Add cream, salt, pepper and nutmeg; heat just until bubbles form around edges of pan, about 5 minutes. Remove from heat; let stand 10 minutes.

Arrange a layer of parsnips, slightly overlapping, in prepared dish. Arrange a layer of sweet potatoes on top, then a layer of celery root. Pour half of cream mixture over celery root; sprinkle half of cheese, thyme and parsley on top. Repeat with remaining ingredients. Cover dish with foil, place on baking sheet and bake 1 hour. Remove foil; lightly press gratin down with spatula. Continue baking until vegetables are tender and top is golden brown, 15-30 minutes or more. Let stand 15 minutes before serving. Serves 12-15.