Celery Root and Potato Gratin Dauphinois

Steps

1. Heat the oven to 350°F. Rub a 9-by-13-inch (or similar 2-quart) baking dish with the cut sides of the halved garlic clove, then butter it generously.
2. Combine the cream, milk, minced garlic, thyme, salt, white pepper and nutmeg in a large, wide pot and bring to a simmer over medium heat.
3. Add the celery root and potato slices and simmer gently 10 minutes, stirring carefully with a spatula every couple of minutes so nothing sticks, until the slices are pliable and the cream has thickened from the potato starch. Remove the thyme stems.
4. Spoon the slices into the dish, shingling them roughly into even layers, and pour over all the cream. Press down so the top layer is just submerged. Scatter the Gruyère over the top.
5. Bake 40–45 minutes, until the top is deep golden, the cream is bubbling at the edges and a knife slides through the center with no resistance.
6. Rest at least 15 minutes before serving so the layers set and the cream thickens.

Kitchen tip

A mandoline makes uniform 1/8-inch slices in minutes; uniform slices cook evenly, which is what makes a gratin melt-in-your-mouth. Do not rinse the potato slices: their starch is what thickens the cream. To make ahead, bake fully, cool and refrigerate up to 2 days, then reheat covered at 350°F for 25 minutes and uncover for the last 10. Traditional Gruyère is made with animal rennet, so use a vegetarian alpine-style cheese if you are cooking for strict vegetarians.

General nutrition information, not medical advice. Talk to your own healthcare provider about your needs.