Roast the poblano and Anaheim peppers on a broiler pan under the broiler, or over a flame until the skin blisters. Put them into a bowl covered with plastic wrap. Allow to sit for about 15 minutes. Peel the skin off, seed and dice. Set aside. (Do not run the pepper underwater as this just dilutes their flavor, a little bit of skin hanging on won't hurt anything.) Dice the jalapeño and Serrano peppers. Place the tomatillos under the broiler until they begin to blister. Remove and set aside.
Meanwhile; pour a small amount of oil in a large Dutch oven; pat the pork dry with paper towels then season them with salt and pepper; begin browning, in small batches, until they are all browned. Remove to a separate bowl as they brown.
Put the tomatoes along with their juice, the tomatillos, the jalapeño, and Serrano peppers along with the cilantro leaves into the work bowl of a food processor or blender; pulse them until coarsely chopped. Set aside.
Heat the oven to 325°F.
When the pork is all browned, lower the heat; add the onions and garlic; saute until the onion and garlic are soft; scraping up any browned bits; (add a little extra oil, or water if the pot is too dry); stir in the flour and sauté for a few minutes; return the meat with any accumulated juices; along with the tomatillo and tomato mixture, stir, add the peppers, oregano, cumin, salt, and pepper. Stir well. Bring to a simmer; cover and place into the oven and cook, stirring occasionally, for about 2 ½ to 3 hours the meat should be very tender. Taste and adjust seasonings. Serve with some good corn and/or flour tortillas or cornbread. Chopped cilantro goes well on top; as well as Cojita cheese.
You could also cook this slowly on the stove-top, although I do find that all-around oven heat just works better; in a crock-pot, a pressure cooker, or Instant Pot. For the crock-pot, cook on low for 8 hours, high for 4, or as your manufacturer directs. If using the pressure cooker, or Instant Pot, cook for 1 hour once pressure has been reached then use the natural method to release the pressure.