Sometimes called Mexican green tomatoes, the tomatillo looks like a small green tomato with a papery covering or husk. It is in the same family as a tomato, but tomatillas have a distinctive tart flavor. For a tomatillo substitute, buy underripe tomatoes and add a squeeze of lime juice.
You will often see tomatillos in Mexican dishes like salsas, tacos, soups, and enchiladas. This swap might work well in a recipe like Slow Cooker Chicken Verde, Ceviche Verde, White Chili with Avocado Cream or Baja Fish Tacos. This rule applies for salsa as well. If you see the phrase "salsa verde", the recipe usually calls for this smaller, more flavorful member of the tomato family.
You can buy tomatillos in Latin-American markets year round as well as in many specialty stores and some supermarkets. The papery covering is removed before cooking.
Recipe: Tomatillo Salsa Verde