Root Vegetable Gratin

Directions

1. 1
   Put oven rack in middle position and preheat oven to 400F.
2. 2
   Butter an 8-inch flameproof ceramic dish or metal baking pan.
3. 3
   Simmer cream, milk, thyme, salt, and pepper, uncovered, in a 4-quart heavy saucepan over moderate heat until reduced to about 3/4 cup, 10 to 13 minutes.
4. 4
   While mixture is simmering, peel celery root with a sharp knife, then cut into large wedges.
5. 5
   Coarsely grate carrots and celery root in a food processor.
6. 6
   Toss with flour in a large bowl until coated well, then add to cream mixture and simmer, uncovered, stirring frequently, 5 minutes.
7. 7
   Transfer to baking dish and smooth top.
8. 8
   Sprinkle evenly with Gruyere and bake until bubbling, about 10 minutes.
9. 9
   Turn on broiler and broil gratin 5 to 6 inches from heat until top is golden brown, 3 to 5 minutes.
10. 10
    Let stand 10 minutes before serving.