Like guanciale, culatello, and lardo before it, pizzaiolo has made it into our robust lexicon of restaurant Italian. We toss it about with relaxed confidence, as if it were a disk of elastic dough.

That we’ve come to speak so knowingly of pizza makers trained in Neapolitan traditions has a lot to do with A16 and Pizzeria Delfina, among the first local outposts to employ not just the term, but also real live pizzaiolos. Now, they’ve been joined by a host of rustic acolytes, the latest being Flour + Water—a first-rate restaurant that, like its forebears, turns out thin-crust pies but has loftier ambitions.

Flour + Water is on Harrison Street, on the outskirts of the Mission district, in a neighborhood as easy for diners to forget as it is for them to find parking in. Owners David Steele and David White gutted the rot­ten inside of a Salvadoran restaurant and fashioned a salvage-chic interior. Wood-beam ceilings overlook a tiny bar and communal seating that give way to a slender dining room with dark walnut tables reclaimed from defunct restaurant Myth. The muted-green walls are sparsely decorated with organic-looking artwork (a painting of a boar skeleton; a mural depicting bony fish), while a skull-and-seashell diorama in the bath­­­room calls to mind a night at the natural-history museum.

You get the drift. This restaurant has an earthy essence, right down to its name (which, in another context, might be taken for that of a warm-up band at Woodstock). Flour and water, those most basic ingredients, provide the raw materials for two of the restaurant’s signature dishes: pizza and pasta. The pies, expertly executed by Jon Darsky, blister briefly in a wood-fired oven, emerging with their edges crunchy, middles tender, and bottoms patterned like leopard skin. The toppings are balanced and restrained (eggplant, olives, and capers; ricotta, arugula, and yellow squash)—nowhere more so than on the margherita, which comes as lightly dressed as (and looks a whole lot better than) the average sunbather at North Baker Beach.

The pizzas are superb, but the pastas may be more appealing still. Conceived by executive chef Thomas McNoughton (a former sous-chef at Quince), they change constantly, ranging from pappardelle in a tangle of mustard greens and braised oxtail to tubular bigoli with pancetta-studded shelling beans. On a recent evening, a rich but nuanced ragù of giblets and brown butter clung to pliant triangles of maltagliati. And crescenza cheese and corn stuffed the pouches of tortellini-like cappelletti, which was drizzled with bitter honey to offset the creamy sweetness of a dish that otherwise might have passed for dessert. There were no stumbles. Whatever shape they take, and whatever sauce they’re paired with, McNoughton’s pastas are perfectly textured; delicate, not dainty; and never chewy, just gently resistant to your teeth.

Flour + Water does well with flora and fauna, too. Salads dare to be different. A fried squash blossom, plump with ricotta, lies atop a scattering of corn and tomatoes, looking like Gulliver amid the Lilliputians. Warm potatoes arrive draped with tender lamb’s tongue slick with salsa verde and the oozing yolk of a poached egg.

McNoughton’s kitchen doubles as a kind of butcher shop; the chef acquires whole animals and makes resourceful use of their less heralded parts. Hence the lamb’s tongue and the cracklings, which were sprinkled one night over a house-carved pork leg, lending a salty spark to meat whose mellow sweetness had been enhanced by slow-roasted nectarines. It was the standout on a short list of solid entrées that included pan-seared halibut with roasted Italian eggplant and a perky olive vinaigrette.

McNoughton also oversees the understated desserts, with the right dash of imagination. Macerated strawberries and candied fennel coax a strong performance out of olive-oil cake, while a faint dusting of basil granità over honey-pistachio semifreddo is a welcome flourish that falls just short of showing off.

With the kitchen in good hands, all that’s left to handle is the human relations—and that’s part of David White’s relaxed domain. The Irish-born co-owner mills about the room, tending to tables as a multitasker, speaking with a Celtic lilt and emanating a warmth that recalls that of an old-world Italian maître d’. White insists so vehemently on a casual mood that his attentive waiters dress in street clothes. The wine service also forgoes formality. Bottles are opened at the bar and sniffed by the staff for infelicities, then delivered to diners for them to pour themselves. The practice feels in keeping with the easygoing spirit of the restaurant, and it’s sure to please the most self-conscious among us, tired as we are of the charade of nosing the cork and swirling the wine with a forced air of concentration before declaring it acceptable.

No wonder lines form early outside Flour + Water, which reserves half of its seating for walk-ins but rarely has enough to go around. It’s what the Italians call a ristorante onesto, an honest restaurant, though it might also qualify as a corsa alla casa base. It is, after all, a home run.

Flour + Water: 2401 Harrison St. (at 20th St.), S.F., 415-826-7000, dinner only, reservation recommended, wheelchair accessible, $$–$$$, 3 stars