Once service starts, Lulu Kitchen & Bar fills fast. One minute, we were seated in an almost empty restaurant, cracking open crab claws as we watched the slow action of Sag Harbor’s Main street. Seemingly the next, every table was full, a line snaked in front of the hostess stand, and would-be diners lurked at the zinc bar, eyeing tables and each other.

Their impatience was understandable: Tables, hard to come by at Lulu, do not turn quickly — in part because you want to linger in the chic space, savoring a whole grilled fish with patina-ed skin or chasing the smokiness of grilled squid with swigs of rosé. But also, servers can tend to go MIA, dishes arrive in languid fashion or checks — or milk, or an extra fork — are a long time coming. If you have patience for this, you will be richly rewarded.

Lulu opened in early May in the former Doppio space, and the face-lift is stunning: A string of elegant rooms lead from open French doors past curved leather banquettes, towering mirrors and a back room of bleached brick walls. In the middle of it all is a quasi-open kitchen anchored by Lulu’s central conceit: a wood-fired oven and grill, long the dream of chef Philippe Corbet. Raised in the French Alps and trained alongside Michelin-starred chefs such as Pierre Marin and Georges Blanc, Corbet has been around these parts since 2001, moving from Long Island (East Quogue’s Stone Creek Inn) to Manhattan (Bouley) and back again. Most recently, he helmed West Islip’s Roots Bistro Gourmand, followed by a stint at Arbor Montauk.

Corbet is not alone in his crush on flame. But the rub is that wood fires can be tricky to work with; Corbet tends his as one would a newborn.

At this, he is masterful. The fire that touches most of the dishes at Lulu is handled deftly, lending a char here or a smokiness there to meat, vegetables and seafood, much sourced from East End farms and fishing boats and handled minimally to elevate their essential natures.

To taste them, though, one must navigate the kinks of a young restaurant. Online reservations are next to impossible — OpenTable yields only late Sunday afternoons, no matter what the request — and the restaurant does not always pick up the phone. One night, we were told there were no meatballs, pizza or burgers. Weekly specials are just starting. There is no cocktail list yet, though a thoughtful wine list is dense with Old-World bottlings.

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Do not pass over Lulu’s raw bar or seafood plates. Crisp, creamy Montauk Pearl oysters come with a pitch-perfect mignonette, and snow-crab claws, called grilled crab cluster on the menu, arrive upright in a cup of melted, herbed butter, their edges charred and the meat steamed to lusciousness. Flames lend tender grilled squid a primal smokiness, though its tentacles were dwarfed by too much frisee. Ditto for a plate of sweet, soft, roasted beets atop a smear of velvety goat cheese — buried under a tangle of citrusy microgreens, and scant for $15. They were gone in a flash, discarded microgreens in their wake. The flesh of a whole grilled branzino, its skin burnished from firing, exhales rosemary and lemon.

Sauces and reductions at Lulu are excellent, such as a puddle of buttery white-wine broth beneath six green-lipped New Zealand mussels, the pesto ringing a silky burrata or the tangy chimichurri spooned over grilled flank steak, an entree. The creamy, bottarga-laced sauce atop tubelike gigli pasta tumbled with clams, mussels, shrimp and crabmeat would have been addictive if the dish hadn’t been lukewarm on arrival; the sauce began to separate quickly. Almost cold to the touch was an iron skillet beneath an otherwise inventive surf-and-turf of lobster claw, charred, maple-glazed corn on the cob and — in a twist — crusty, coppery baby back ribs.

At Lulu, dishes exude comfort in a way that rarely seems overworked. Some of those stick in your memory; others — such as the brittle house bread, a plodding pizza or a $23 burger that’s not quite worth the sticker price — are forgettable. Portions are petite, temperatures not always consistent, and waits can be long. Somehow, though, there is still a magic to this honest, unfussy food stripped back to its essence, likely making seats here hard to come by for the rest of the summer.