In a large skillet over medium heat, break up ground beef and cook until browned, then mix in salsa, beans, tomato paste, corn, and taco seasoning; continue to simmer 5 minutes.
Preheat oven to 375 F. In a deep 9x13-inch baking dish coated with cooking spray, layer in this order: 6 tortillas (cut some in half to fit), a third of the meat, Monterey Jack cheese; 6 tortillas, a third of the meat, half the cheddar cheese; 6 tortillas, remaining meat, remaining cheddar cheese. Loosely tent with aluminum foil and bake 20 minutes. Remove foil and bake another 5 minutes to fully melt the cheese. Let rest 5 minutes for layers to set before cutting. Serve topped with sour cream and cilantro (optional).
Per serving: 646 calories, 25 grams fat (11 grams saturated fat), 66 grams total carbohydrates, 1,219 milligrams sodium, 96 milligrams cholesterol, 7 grams fiber, 38 grams protein.
