Cut the tortillas in half and set aside.

In a pot, cook the chicken breast with onion and cilantro.

Roast the poblano peppers directly over the flame or on a grill. Wrap them in a towel, place in a bag, and let them rest for 10 minutes. Remove from the bag, peel off the skin, remove the seeds and veins, and cut into strips. Set aside.

Blend the tomatoes, garlic, cilantro, 1 tablespoon salt, and a little black pepper. Add some of the chicken cooking broth to make a sauce that's not too thick—prepare about 6 cups of sauce.

Slice or shred the Manchego cheese. Set aside.

Cut the remaining half onion into thin strips and sauté in a pot with hot oil. Once translucent, add the chicken bouillon, tomato sauce, and epazote. Cook the sauce until it turns a rich red color.

Grease a large baking dish with butter. Dip the tortilla halves in the sauce and layer them in the dish, alternating with shredded chicken and poblano strips, then a layer of cheese, finishing each layer with a little more sauce. Repeat until all ingredients are used. Finish with a layer of cheese and, if any remains, pour the last of the tomato sauce on top.

Bake for 20 minutes at 350°F (180°C), or until the tortillas are well set and most of the moisture is absorbed.