Cut tortillas in thin strips with scissors or a knife.
Saute them in 1/3 cup lard until crisp, but do not brown.
To make sauce, saute onion in 2 tablespoons lard until transparent; add chilies, cream, and tomato puree.
Simmer for 10 minutes; add salt to taste.
Grease a 2-quart baking dish and cover bottom with half the tortilla strips.
Pour over half the sauce and add a layer of half the shredded cheese.
Repeat layers, ending with cheese.
Dot with butter and bake in a moderate oven (350°) for 30 minutes.
Makes 6 servings.