Costanera spices up Montclair’s culinary scene with an interesting, authentic Peruvian menu, but the newbie hasn’t quite worked all the kinks out just yet. The BYO restaurant, which opened in May in the space formerly occupied by Udupi, shows bright and low spots, both on the plate and off. Chef Juan Placencia is certainly no stranger to the kitchen, having trained at the Culinary Institute of America and held posts at three of New York City’s most notable restaurants: Jean-Georges, Del Posto, and Gramercy Tavern. Several of the dishes from Placencia’s mainly seafood menu showcase his expertise with fish, particularly the Tiradito Tradicional ($14), a Peruvian mahi mahi sashimi which is sliced thin and dressed with a citrus-based aji rocoto cream. The lovely, light dish is refreshing, with bright, clean flavors more reminiscent of a ceviche than a Japanese sashimi.