Blackened rare ahi tuna steak at Masa

It must be trying to be the Boston ambassador for an obscure cultural import. Pity the Brazilian gatinha who must endlessly explain her keratin hair-straightening regimen to norteamericana girlfriends, or the British Premier League fanatic whose Yank buddies have only heard of Beckham. As cosmopolitan as Bostonians fancy ourselves, we have our blind spots. Take Southwestern cuisine, which we often lump in with Tex-Mex, missing the distinctive regional subtleties: its use of myriad chile peppers; its Native American foundation in squashes, legumes, and maizes; its recent fusion with European techniques to form a sophisticated nueva latina style of cooking. The folks at Masa (439 Tremont Street, Boston, 617.338.8884), the veteran South End hot spot, must inwardly cringe when customers ask where the nachos and burritos are.

But that ignorance hasn't prevented us from packing into Masa's often screamingly loud bar, which features the city's best selection of tequilas (with over 100 bottlings), tremendous cocktails (like a $10 Margarita made with habanero-infused tequila and watermelon puree), and the steal that is its tapas combo platter ($10, $5 from 5 to 7 p.m. daily and all night on Thursday), a plate of 10 drink-friendly bar bites like chicken taquitos and pulled-pork spring rolls. The quieter dining room, a magnet for date night, boasts casually pretty Santa Fe-themed décor: white-painted brick and terra-cotta, bronze, turquoise, and mirrored accents diffusing the soft lighting. Service is relaxed, prices gentle. A field greens salad ($7.95) intrigues with unusual accents like Cabrales (a creamy, intense blue cheese), crunchy jicama, chile-dusted cashews, and chewy dried strawberries. Pureed butternut squash chowder ($6.95) avoids the typical over-sweetening, instead opting for exclamation points of smoke and salt in an island of poblano pepper strips, smoked Gouda, and stunningly flavorful lardons.

The Southwest's affinity for big cuts of meat shows in a chile-rubbed Frenched double-rib pork chop ($25.95), which is actually far more elegant-looking than it sounds, though its accompaniments (huge onion rings, grilled baby corn, and mashed potatoes) add cowboy-worthy heft. Another fine example of the sophisticated sensibility of chef-owner Philip Aviles and his executive chef, Gregory Stevcic, is an entree of blackened rare ahi ($23.95). Anchored by earthy notes of roasted potatoes and wild mushrooms, this barely seared, gorgeous hunk of tuna is superbly complemented by a rich, complex yellow mole - layering flavors of chiles, garlic, and sweet spices - that tastes like it took days to make. That combination of creativity, depth, and lightness, so far from the sizzling-fajita and melted-Monterey-Jack clichés of border food, is a pleasant shock to many first-timers, and doubtless a big part of what keeps them coming back.