Bring a pot of water to a boil. Put the chilis in a non-reactive bowl. Pour the boiling water over them. Soak until soft, about 1 hour, then drain, reserving the soaking water.
Place chiles, garlic, onions, and 2 cups of the soaking water in a blender. Purée until smooth. Thin with more soaking water if the sauce is too thick.
Put the sauce into a saucepan. Add cumin, garlic, and oregano. Taste for seasoning. If it seems too bitter, add a pinch of sugar. Simmer, uncovered, over low heat for 10 minutes or until the sauce has thickened.
Enchiladas
Shred the cabbage in a food processor, then put it in a large bowl.
Shred the cheese in the food processor and add them to the bowl.
Finally, chop the onion in the food processor and add it to the bowl. Lightly mix the cheese, onion, and cabbage together.
Put 2 to 3 tablespoons of the sauce on the bottom of the casserole. Put a layer of tortillas on top of the sauce. Cover the layer with some of the cheese mixture. Spoon a little of the sauce on the cheese, then top with more tortillas, cover with the sauce, to make a second layer, then cheese, then the tortillas are last. Pour the remaining sauce over the casserole.
Sprinkle Cotija cheese over the top of the casserole. Bake in a 350 °F (177 °C) oven for 30 minutes or until the sauce is bubbling and all the cheese has melted.
Garnish with more cheese, chopped cilantro, and green onion as desired.
Serve with sour cream.
Scan for full nutrition info and step-by-step photos.