Sautee onion & garlic till translucent. Add all remaining ingredients except the cornstarch & simmer on low heat until potatoes are tender & chiles fall apart easily --about 45 minutes.
Mix cornstarch with about 3/4 cup cold water, whisk till smooth. Turn up the heat, whisk cornstarch mixture into sauce & bring to boil. Boil about one minute more till thickened.
This dish gets spicier as it ages, so if you're sensitive to hot food, cut back on the cumin.
Great over bean burritos, enchiladas, rice, just about anything! I serve with a dollop of Rice Sour Cream Replacement (vegan) mixed with a little Veganaise. Terrific!