Tomatillos are a firm, round fruit encased in papery husks. The flavour resembles that of tart apples with a hint of lemon. Smaller ones, about the size of a walnut in a shell, have more concentrated flavour. Used in table salsas and in green tomatillo sauce (salsa verde), which is poured over enchiladas before they are cooked. They are hard to find so you can substitute with ripe tomatoes. Canned tomatillos are available at some supermarkets and speciality food stores.