Rice vermicelli are sold in nests, which can be tricky to separate without breaking the noodles into shards. Instead, cook the whole package and save any leftover vermicelli to use in a stir-fry, soup or noodle salad. Fish sauce, known as nuoc mam in Vietnam, is usually made from fermented anchovies. For a fresh, clean flavor, look for one that doesn't contain preservatives, like sodium benzoate.