As Rosa has expanded nationally over the years, its upscale take on Mexican standards has dissipated somewhat. But surprise, surprise: The cuisine at the new South Beach branch boasts strong, cleanly defined flavors; the service staff works with relay-team efficiency; and a festive ambiance prevails. Among starters, don't miss the red snapper tostadas: lime-macerated cubes of fish sprinkled with baby arugula leaves, queso fresco, Serrano chilies, truffle oil, and bacon crisps. Zarape de pollo rocks too, with moist, sassily smoked-and-seasoned morsels of chicken sandwiched between two corn tortillas and bathed in yellow-pepper/habanero sauce. A basket of corn tortillas with pronounced notes of corn and slaked lime come alongside juicy strips of carne asada in a mini-cast-iron skillet with melted Chihuahua cheese - a make-your-own taco kit. Vegetarians can build their own tacos from a skillet of mixed vegetables, red beans, and flax-seed tortillas. Rosa's mellow mole Veracruz is one of the better restaurant versions, here bathing shredded beef enchiladas. A more unusual treat presents two roasted ancho chiles rellenos swelled with shredded lamb shoulder and cabbage in pipián sauce. Other main plates ($15 to $27) include short ribs, pork shank, and steak and shrimp stew. Desserts ($7.50 to $8.50) are prepared in-house by pastry chef Jai Kendall. Banana chocolate-chip cake funneled with peanut butter mousse and topped with chocolate syrup and cinnamon-swirled banana ice cream might sound a bit overwrought, but just say yes.