Chop up the onion and mince the garlic. Add a couple of tablespoons of water to the pan, heat it up and cook the onion and garlic until aromatic and soft. Add the tomato sauce, the rest of the water, and the salt and spices. Bring the sauce to a boil, lower the temperature, cover and simmer for about 20 minutes.
Mix the cornstarch with the water until there are no lumps. Add to the sauce. Raise the temperature until it boils, stirring constantly. When thickened, the enchilada sauce is done.
This recipe makes enough sauce for a 9 x 13 pan of enchiladas. See our video Asparagus and Zucchini Enchiladas for directions to make vegetable filled enchiladas.
Store unused enchilada sauce in the refrigerator in an air-tight container for up to a week or in the freezer for several months.