As usual, Sushi Gen has a line out the door. Even at 6 p.m. on a Tuesday, the immensely popular Little Tokyo sushi house has groups of customers waiting outside, fidgeting with their phones, clogging the parking lot. The 3-month-old restaurant next door, b.o.s., has no such problem. Over the course of the following hour or so, as the crowd outside Sushi Gen grows, only two tables are occupied in b.o.s.' small dining room.

Opening a restaurant next to one of L.A.'s favorite eateries must be somewhat difficult, like the plight of a dorky younger sibling stuck in the shadow of her wildly popular teenage sister. But b.o.s. is hardly nerdy — in fact, this is one of the more ambitious restaurants to open lately. Hyper-modern, Asian-influenced, and serving a menu made almost exclusively from the offal of cows, this small, moody restaurant might easily end up with out-the-door lines of its own one day, if L.A. develops the same hankering for creamy calf brains as it has for the glistening slivers of hamachi served next door.

Reading over the menu at b.o.s. is like perusing the meat counter at one of those grocery stores that serves Mexican, Filipino or Chinese communities, a store whose customers might need any and all parts of an animal and so has any and all parts on hand — except in those stores you'd see goat heads and pig's feet. Here the focus is solely on beef.

The restaurant's name, pronounced “boss,” comes from the Latin word for cow, ox or bull, and its menu offers steak, ribs, brain, tripe, tendon, bone marrow and heart. There is no roast chicken, no delicate fish dishes, not even a sticky slab of pork belly, that meaty treat that used to be considered audacious but now is about as common as pork chops.

There are a few vegetable dishes as a concession to those who don't want an all-offal dinner, but other than that it's all beef.

Fittingly for this theme, a painting of a cow on the wall is made from words that describe its innards (and out-ards). Its back leg, for instance, begins with the words “udder” and “beast,” and ends with “Kobe” and “feet.”

B.o.s. is a project of restaurateur Jun Isogai and chef David Bartnes. Bartnes is not from Los Angeles, but his background and cooking style make L.A. a natural fit. Born in Oregon and raised in Asia and Europe by a Chinese/Japanese/Korean mother and German stepfather, Bartnes trained at Le Cordon Bleu in London before embarking on a career that entailed working for Hilton in Shanghai, as well as other endeavors across Asia and Europe. Eventually he landed here, and was recently the executive chef of the L.A. Marriott downtown.

This new restaurant is a very different venture for Bartnes. Where hotel menus are vast, b.o.s.'s is small and focused. Where hotels aim to please all the people all the time, at b.o.s. Bartnes is serving exactly what he feels like: food that only offal lovers and culinary adventurers are likely to appreciate.

His gung-ho attitude toward the more fiddly bits of our bovine friends is, frankly, refreshing. What Bartnes turns out from his open kitchen isn't always brilliant — in fact, some of it doesn't work at all. But in recent months I've found myself saying to people, “Right now I'd rather have something uneven and unexpected than something perfect and predictable.” So, yes, what Bartnes is delivering can be wildly uneven, but there's just as much that does work and is blessedly unexpected.

There are dishes here that bowl you over with originality and nerve, like grilled heart, marinated in miso and served crispy on the outside and rare as blood on the inside. Jumbled with the slivers of heart are deeply smoky king oyster mushrooms, which have been grilled over traditional Japanese binchotan charcoal with some wood chips thrown in for extra smoke. It's a dish that considers the flavor and character of the meat, which plays up its very best qualities — its rich minerality, its firm texture — and provides a lovely contrast with the soft, sweet smoke of the mushrooms and a tart yuzu miso vinaigrette. It's one of the best heart dishes I've ever had.

The beef carpaccio is made of tongue, sliced as thin as tissue and topped with a smattering of pea sprouts and tiny cubes of avocado. Served in this way, the tongue loses any hint of the musk that defines it when cooked; instead it becomes a mellow, delicate amalgamation of satinlike meat and fat.

Crisp, curried calf brain has the most outrageous texture, creamy and tender and practically liquid in its center, and sporting a shattering outer layer of savory panko.

The short rib, which comes on the bone and melting with fat content, is described as “Hunan-style,” meaning its outer layer is coated in cumin and chili. It's served over a bed of hearty kale, which acts as a nice foil to the soft meat, and olive oil–poached pee wee potatoes that take on an edge of vanilla, which is quite odd but also quite good.

Lest you think you're getting off easy when ordering the cherry tomato and burrata salad, the one menu item that on first look seems to fall in with current trends, think again. Those tomatoes, along with deep purple beets, come buried in what can only be described as burrata foam, a bowl of creamy, aerated cheese with much the same consistency as shaving cream. I'm not sure this presentation does much for the flavor of the thing, but it sure is fun.

And what of that unevenness? Is there any reason to serve a mediocre sweetbread taco when there are so many amazing sweetbreads, and so many amazing tacos, to be had elsewhere? Yet the one offered here just isn't a very good taco, the tortillas and salsa and Sriracha sour cream failing to become anything other than flat and predicable, no matter what meat lies within.

Bone marrow comes topped with furikake, a Japanese dried-fish condiment that Bartnes makes in-house, and served with a circulated egg and Korean chili paste smeared across the plate in a manner that's quite appealing visually but hard to consume, practically. Sadly, the marrow itself had that unfortunate past-its-prime flavor, one I can only describe as skanky, and the circulated egg was just too texturally similar, all wobble and goo. Despite the thought and effort put into this dish, it simply doesn't work.

I felt similarly about the tripe and kimchi stew, which actually has very little tripe in it and more shredded stewed beef, as well as oddly leaden scallion gnocchi and another circulated egg. It's one of those dishes with too much going on; not bad, but just not good enough for the confusion it creates.

I'd caution you to stay away from dessert altogether — it's the one place where Bartnes' hotel cooking background shines through, and not in a good way.

But when it comes down to it, I'm grateful for a chef and restaurateur willing to be this bold, and willing to do something that, truly, no one else is doing. It's worth the occasional dish that doesn't quite work for all the food here that's both surprising and delicious, especially at prices this reasonable and in a room this welcoming. Go now, before people realize that most of what Bartnes is turning out is, in fact, food worth standing in line for.

b.o.s. | Two stars | 424 E. Second St., dwntwn. | (213) 700-7834 | | Tues.-Sat., 5:30-10 p.m. | Plates, $10-$18, large plates $28-$36 | Beer, wine and sake | Lot and street parking

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