In skillet cook onion in lard till tender but not brown.
Blend in flour.
Add milk, chili peppers, and salt.
Cook, stirring constantly, till thick and bubbly.
Stir in beef and tomatoes; heat through; keep warm.
In small skillet heat tortillas, one at a time, in hot oil till limp, about 15 seconds per side Drain on paper toweling.
Place a hot tortilla in 9x9x2-inch baking pan.
Top with about 1/4 cup beef mixture and a small amount of cheese.
Repeat with remaining tortillas, beef mixture, and cheese to make a stack.
Bake at 350° till hot, about 20 minutes.
Unstack to serve.