After 30 minutes, whisk together the masa harina with 1 cup of water. Stir the masa into the chili, along with the lime juice and the green chilies. Stir and cook until thick, about 5 minutes.
TIP: Masa is Spanish for “dough” and is traditionally used to make corn tortillas. Masa is a thickening agent that also adds natural corn flavor. Masa harina is flour made from the dried tortilla dough.
To get that distinctive flavor, try grinding stale or dry corn tortillas in a food processor until you get a fine powder. If the masa harina is used as a thickener (such as in chili), regular flour or cornmeal will give you the right texture, though the flavor won't be quite the same.
If you can’t find masa harina, use 2 tablespoons of corn starch instead.