1 pound celery root thick peeled very thinly sliced ()
2 garlic clove peeled
2 cups gruyere cheese grated
3 cups cup heavy whipping cream
10 servings kosher salt
3 leek white halved lengthwise thinly sliced
2 pounds baking potatoes thick peeled very thinly sliced ()
1 sprig thyme leaves fresh divided
2 tablespoons butter unsalted divided ()
Equipment
bowl
sauce pan
oven
aluminum foil
Directions
Preheat oven to 350°F.
Heat cream, garlic,and thyme sprig in a medium saucepan justuntil bubbles begin to form around edge ofpan.
Remove from heat; set aside to steep.
Melt 1 tablespoon butter in a medium skilletover medium heat.
Add leeks; season withsalt and cook, stirring often, until tender (donot brown), 10-12 minutes.
Transfer to asmall bowl and set aside.
Butter a 3-quart gratin dish with remaining1 tablespoon butter.
Layer 1/3 of potato slices and1/3 of celery root slices evenly over bottom ofbaking dish. Cover with 1/3 of leeks, then 1/3of Gruyère.
Sprinkle with salt, pepper, and1 teaspoon thyme leaves. Repeat layers twicemore. Strain cream mixture into a mediumpitcher and pour over vegetables.
Set gratin dish on a large rimmed bakingsheet and cover tightly with foil.
Bake for1 hour. Carefully remove foil; continuebaking until top is golden brown and sauceis bubbling, 25-30 minutes. DO AHEAD: Canbe made 2 hours ahead.
Let stand at roomtemperature. Tent with foil and rewarm in a300° oven until hot, about 20 minutes.
