Shaking the tree at the Argentinian aerie called El Arbol

A lot of Argentinian food wears its influences on its sleeve, its European roots on full display. But beef is where the heart is.

And man, do I (heart) the 14-ounce shell steak at El Arbol, the Argentinian restaurant that opened in February off West 35th Street. The size of a fat baked potato and cut from the beef short loin, the shell steak carries the texture of tenderloin and the robust flavor of a strip, seared a uniform mahogany brown, crowned simply with chimichurri. If El Arbol were a formal steakhouse, that might be enough.

But El Arbol is anything but a leather-locked house o' beef. It's a three-level South American treehouse insinuated around a sprawling oak with more twists, side-branches and shadings than a Jorge Luis Borges story. Whenever I mention El Arbol, people already know the building, having watched it grow like an enigmatic child for two years, rising from a shell that once was a family home, then a series of offices.

Designed by mid-century interpreter Joel Mozersky and architect Aubrey Carter, El Arbol is owner Andrew Sorrell's celebration of split-level, late-'50s cocktail culture. Inside, the first floor echoes diner style, with white leather booths and screen dividers with extruded diamond patterns. The bar on the second level glows from within, sharing the floor with a boozy formal dining room set with dark, button-plush leather in speakeasy lighting. It will remind you of another Mozersky design, the Rat Pack den called the Belmont, if the Belmont had been transported to a moneyed quarter of the sunlit Southern Hemisphere.

Seating at El Arbol is more outside than inside, the first two decks in step with the higher style of food (except for the TVs), the third level functioning as a beach bar with a killer view of the Burger King parking lot next door, from which we watched an SUV being towed, and I wondered if somebody sipping a caipirinha was about to have a bad night. El Arbol has no real on-site parking, just a few spaces from which a valet service operates, and street parking fills up early in this residential area.

A good way to find a spot and shake 'The Tree' is during a 5 to 7 p.m. happy hour Tuesdays through Thursdays, when appetizers are half-price. You could try them all for $26.

With a dusky malbec wine reduction, one of those appetizers is a protein hand grenade called a matambre ($12), a low-carb carnivore's delight of thin sirloin rolled around spinach and boiled egg. Ceviche here is made with whitefish in pieces the size of cherry tomatoes, with a fresh taste amplified by mild onions, red and yellow peppers and a splashy citrus bite ($11).

Most intriguing was Anticucho de Corazon ($9), thin ribbons of beef heart threaded onto metal skewers. It's nothing like what you'd expect, drawing most of its flavor from chili oil and a sweet balsamic syrup, most of its aroma from grilled onions. In a way, the dish felt like a missed opportunity to taste the unfamiliar cut of meat on its own terms.

The real heartbeat of chef Chad Dolezal's kitchen at El Arbol is oak-grilled meat. Steaks start at $22 for a five-ounce filet and rocket to $63 for a 32-ounce rib-eye.

Food from the grill - which in addition to steaks includes sausages, veal sweetbreads and chicken - gets a trio of small dishes on the side. In one bowl, there's chimichurri, a traditional South American marinade and grilling sauce of olive oil, vinegar, herbs and pepper flakes. In two more small bowls are daily 'tasting sides,' quarter-cup servings that on different visits included cold asparagus with lemon, strips of roasted pepper, an outclassed cucumber-grape salad and spackly polenta with Brussels sprouts.

As excited as I was to tell people about El Arbol, I stumbled on my own hallelujahs when I mentioned the sides. It's easy to like a $30 shell steak when your boss is picking up the tab, but most people want a real starch or vegetable for that price, not a few precocious nibbles. Additional sides - spinach in Hollandaise sauce, fries, mashed potatoes - run $4 to $7.

Not everything can be beef. It could, but the cattle would catch on after awhile. To throw them off, there are $3 empanadas with pork, raisins, olives and almonds and ones with spinach and cheese, like hand-crimped half-moon pies with shells like lacquered pizza crust.

There's rabbit, and on Tuesdays, a pork chop. The rabbit is rangy and unfamiliar, served on the bone and with a small saddle piece alongside potatoes for $25. The natural lean dryness of the meat works well with a braising stock that conveys the mirepoix flavors of carrot, celery and onion. Like the meat, the value seems a little lean, the same with an $18 Tuesday pork chop special, a modest bone-in piece glowing orange with chile and crossed like a Modernist canvas with black, double-striped grill marks, served with those mostly decorative tasting sides.