Step 1Season the pork with salt and pepper. Heat 2 tablespoons oil in a Dutch oven. Add the pork shoulder and sear on all sides. Pour 2 cups chicken broth into the pan and cover. Place in a 325-degree oven and cook until the meat is extremely tender and easily pulled apart with a fork, about 2 1/2 to 3 hours.
Step 2Heat the remaining oil in a large skillet. Add the onion, garlic and tomatillos and cook until soft, about 5 minutes. Add the peanuts and the raw pepitas and cook for 2 more minutes. Add the cilantro, epazote, lettuce, tortilla pieces, bolillo slices and chiles. Stir in the remaining chicken broth and bring to a boil. Reduce the heat and simmer until the chiles are soft and flavors have blended, about 15 to 20 minutes.
Step 3Let the mixture cool slightly, then blend in batches until smooth. Add a little water or broth (one-fourth to one-half cup) if necessary to make a thick but pourable sauce.
Step 4Return the sauce to the pan and heat to serving temperature. Season with 1 1/2 teaspoons salt or to taste. Makes 6 cups sauce.
Step 5To serve, shred the cooked pork and arrange on a serving platter. Pour the sauce over the top and sprinkle with pepitas.