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Celeriac and potato gratin

Time1 hour 15 minutes
YieldsServes 6 to 8
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I once spent a year trying to cook only what was locally in season and wound up hooked on a lot of peculiar produce. Sometimes the relationship was like the Stockholm syndrome -- I had to appreciate Jerusalem artichokes in darkest winter -- but with celery root it was a clear case of vegetable attraction.

I already knew the knobby root from celeri remoulade, the quintessential first course in pate-prone French restaurants, which is one of the best destinations ever booked for it. But in the long months when it was about the only alternative to squash and potatoes in the farmers market, I cooked it over and over and learned you can do things with it that you would never try with real celery.

The root is formally known as celeriac and is, in the inimitable words of produce passionista Elizabeth Schneider, “a variety of branch celery cultivated for its lowers rather than its uppers.”

Waverley Root also weighed in wittily, saying the bulbous vegetable was developed in Renaissance times by gardeners “who persuaded celery to become a turnip.”

Neither description really conveys its appeal, though: The root, a cousin of carrots in the umbel family, has a unique taste, with hints of parsley and celery and something undefinable. Raw or cooked, it keeps that flavor -- a little bit sweet, a little bit nutty.

The root looks more like something left behind by aliens than a promising source of kitchen inspiration. Depending on how manicured the produce dealer presents it, it may have green stalks attached to the top or finger-like roots wisping off the bottom, or sometimes even hair-like tendrils covering it. It can be gnarly or smooth, soil-crusty or wiped clean.

But the creepiness is only skin-deep. Once you pare away the outside, you have a firm, fat, cream-colored vegetable ready to be julienned, simmered, braised or baked. The crunchy texture is half of its appeal in celeri remoulade, with the lemony, mustardy dressing acting as something of a tenderizer.

Cook the root soft enough, though, and you can just puree it with cream as a side dish, or you can blend it with broccoli, or mix it into regular mashed potatoes for a much more nuanced starch.

Chefs, even the most inspired, tend to see celery root as only a leading candidate for soup. Their concept is on menus everywhere, a basic puree made with stock and cream and maybe aromatics like leeks or a thickener like potato. But in the end, it’s just soup.

Far more interesting and much less ubiquitous are celeriac pancakes. I make them by grating the peeled root, mixing it with an equal amount of grated russet potatoes, then shaping it into patties to fry until they’re crisp outside, super-soft inside, about 15 to 20 minutes total. You don’t need egg for a binder or anything else beyond salt and pepper; a little walnut or hazelnut oil for frying adds all the complementary flavor you need. Like any fried food, though, celery root pancakes don’t object to a little creme fraiche or sour cream garnish.

Because celery root goes so well with rich partners, baking it in a creamy gratin with sliced potatoes is the easiest way to bring out its best. There are dozens of ways to do that, but I’ve found it’s most foolproof if the two vegetables are cooked separately first, then combined in a baking dish with the cream, stock and cheese.

Traditionally, the cheese is Gruyere, which echoes the nuttiness of the vegetable. But you get more depth from stronger, muskier goat cheeses, like Dutch Arina, a type of Gouda, or mellow blue cheeses, like Maytag or Gorgonzola.

There are only a couple of tricks for cooking with celery root. Buy the firmest specimen you can find -- once the roots go soft, they turn woody inside. And the flesh will turn a nasty brown once it’s cut, so you have to either toss it with something acidic (usually lemon) or cook it in a blanc, a mixture of flour and water.

The root should also be scrubbed before cutting. Roger Verge, in his singular “Vegetables in the French Style,” inspired me to recycle the trimmings, which have tons of taste, by either adding them to stock or soup or by hanging them to dry and grinding them to make celery salt. (It works.)

As with any great ingredient, celery root always encourages you to experience it in new ways. I was chopping one up recently while a wedge of the new Midnight Moon cheese from Humboldt Fog was in the vicinity and decided to use a slice of celery root as a “cracker.” The combination was stunning, and for once I could see what regular celery is reaching for when it lies down with Cheez Whiz.

1

Place the celery root in a saucepan and add the milk and salt to taste. Sift the flour over the top. Add enough cold water to just cover the slices. Bring to a boil, reduce the heat and simmer, uncovered, until the slices are just tender, 5 to 7 minutes. Drain well and set aside.

2

Place the potato slices in a second saucepan, add salt to taste and water just to cover. Bring to a boil, reduce the heat to medium-high and cook until just tender, about 5 minutes. Drain well and set aside.

3

Heat the oven to 375 degrees. Butter a 10-inch round gratin dish and rub well with the cut garlic. Arrange the celery root and potato slices in the pan in alternating layers, starting and ending with the celery root and seasoning each layer well with salt and pepper. Combine the cream and stock and pour evenly over the potatoes. Sprinkle the cheese evenly over the top. Bake until the liquid is absorbed and the vegetables are easily pierced with a knife, 30 to 35 minutes. Then place the dish under the broiler until golden brown and bubbling, 2 to 3 minutes. Cool slightly before cutting in wedges to serve.