After eating my way through the bulk of the pastry and dessert case at Petrossian, I've come to a fairly simple conclusion. Nearly everything here is good, if not great. They have my favorite fruit tarts in the city and a killer pistachio croissant, along with excellent canelés. While you're here add this Pistachio-Chocolate Mousse ($7.50) to your must-purchase list. It's a teardrop-shaped creation, equal parts milk chocolate mousse and pistachio mousse. Both elements are light, almost airy, with bold flavors, together finished in a sprinkle of ground toasted pistachio nuts. Equally appropriate at the dinner table or wolfed down right outside the shop.