Wipe off any dusty crevasses on the Anchos, then de-stem and de-seed them. Roast them in the oven at 400F for 1-2 minutes. Cover the Ancho pieces with hot tap water and let reconstitute for 20-30 minutes
Roast 2 tomatoes in the oven at 400F. They'll be mostly roasted by the time the Anchos are done reconstituting.
Roughly chop 1 medium-sized onion. Set aside 2 tablespoons of the onion for the inner mixture of the enchiladas. Saute the onion in a dollop of oil over medium heat along with the 2 whole, peeled garlic cloves. Cook until lightly browned.
Drain the Ancho chilis. Add the chilis, tomatoes, onion, garlic, and 2 cups of stock to a blender. Blend until smooth. Strain the blender sauce through a fine mesh sieve and discard the leftover seeds and skin.
Saute the strained sauce in a dollop of oil over medium heat. Add 1/2 teaspoon cumin, 1 teaspoon Mexican oregano, 1/2 teaspoon of salt, and some freshly cracked black pepper. Let simmer for 30-45 minutes or until it reduces down to a thick, velvety consistency.
You can use rotisserie chicken for the enchiladas, or now you can start poaching 2 chicken breasts. Simply cover 2 chicken breasts with cold tap water, bring to a boil, then reduce heat to let simmer for 20-25 minutes or until cooked through. I typically salt the poaching water and for this batch I added pepper, onion, and cilantro to the pot. Once the chicken is cooked, set aside to cool and then shred it using two forks.
Warm the tortillas in the oven for 1-2 minutes or nuke them in the microwave for 60 seconds.
To build the enchiladas, start by adding a few tablespoons of the enchilada sauce to a plate. Dredge a tortilla in the sauce and flip it over. Fill with chicken, cheese, and finely chopped onion. Roll tight and set them seam side down in a baking dish (You can add some sauce to the baking dish to prevent sticking). Continue rolling the enchiladas but be sure to save enough sauce to cover the tops of them generously in the baking dish.
Bake the enchiladas for 10-15 minutes in a 400F oven.
Serve immediately. Optional garnishes include Cotija cheese, cilantro, and Crema.