A tomatillo (Physalis philadelphica) looks like a small green tomato covered with a pale green leaf or husk. In fact, the name tomatillo means “little tomato” in Spanish, and the fruit is indeed related to tomatoes, both being a part of the nightshade or Solanaceae family. They are close relatives of the Cape gooseberry (not a true gooseberry) and the Japanese Lantern fruit (bladder cherry). All of which are in the genus Physalis.
Tomatillos are very popular in Mexican and Southwest cooking.
The fruit, which tends to be around 1.5 to 2 inches in diameter, ripens from a pale green to a yellow color, but tomatillos are almost always used when green, when their unique flavor is at its height. Some varieties, however, are purplish in color.
Although the fruit looks like a little green tomato, the flesh is much firmer and has a tangy flavor all its own, with lemony and spicy herbal overtones. They come in two basic varieties, sweet and sour (acidic). Both are widely available in the U.S.and are available all year. The plant grows wild in California.
The husk, called a calyx, is easy to remove, but leaves a sticky residue that has to be washed off before the fruit can be used. To facilitate removal of the husk, soak the tomatillos in warm tap water for a few minutes. Before using, remove the stem and core with a paring knife or other implement.
Tomatillos are central to the flavor of salse verde, and many other Mexican and Central American cooking. They can be used raw, but they are usually cooked, including when used in fresh uncooked salsa (salsa cruda, or salsa made with raw vegetables or fruit). Cooking softens the texture and deepens the flavor of the fruit.
When you purchase tomatillos at the grocery store, the husk will probably be light brown and slightly opened. Make sure the fruit underneath is a fairly uniform light green color with a firm texture. Avoid yellow or soft tomatillos unless you have a recipe that specifically calls for yellow, more ripe, fruit. Mexican cooks sometimes pull up entire plants and hang them upside down in a dry place, with the fruits still attached. In this way, they may last for months.
It is best to use tomatillos as soon as possible. If you need to store them, leave them in their husk and place them in a paper bag in the refrigerator for up to one month. They can also be frozen for long-term storage.
In Mexico, the tomatillo is also known as milto-mate, tomate verde, tomate de milpa, fresadilla, or even just tomate. They are also called Mexican husk tomatoes and like many members of the genus Physalis, ground cherries. The tomatillo was probably more often consumed during ancient time than the sweet red tomato or jitomate and has been cultivated in Mexico since pre-Columbian times.