Chic and minimalist, Castagna's dining room is a handsome blank frame for food that manages to be both traditional and subtly innovative. One might be tempted to make a meal of the starters: a housemade pork-and-pistachio p�t�, delicate pasta purses stuffed with duck and porcini, or the "trio" of carrot confetti, roasted beets and a sort of pommes frites made of mashed garbanzos. Entr�es are more sedate and hearty, but no less tasty: Familiar saut�ed salmon tastes new again in its sumac crust, and the only fault of the pan-seared lamb chops crusted with Parmesan was the skimpy portion. Servers are knowledgeable about everything from preparations to the provenance of the ingredients. The crowd is a blend of the well-heeled and the hip, a demographic mix reflected in the menu; Castagna can be as spendy as you can afford, but there's also a three-course prix-fixe for $28. (KA)