The menu of the tiny Tremont restaurant Ushab, which opened in October 2016, centers around shabu-shabu. That’s a traditional Japanese variety of hot pot where diners dunk chosen ingredients in a simmering pot of broth with a focus on thin-sliced meats and seafood (although a vegetarian version is available), then flavored with a variety of sauces. A menu of small plates is also available. The spare, angular space is very small so reservations are recommended. It’s open for lunch Tuesday through Saturday, and dinner Tuesday through Sunday.