Stir together the flour, 1 teaspoon salt, pepper, and cumin in a large bowl.
Place the cubed pork into the mixture, and stir well to coat the meat with the seasonings.
Heat the olive oil in a large, heavy pan or Dutch oven over medium-high heat until the oil shimmers.
Working in batches if necessary, place the meat into the hot pan in a single layer. Panfry the pork until brown on all sides, about 15 minutes.
Remove the pork to a bowl, and cover to keep warm.
Cook and stir the onion in the hot pan over medium heat, adding more olive oil if necessary, until the onion is translucent and beginning to brown, about 7 minutes.
Return the meat to the pan and stir in the garlic, tomatillos, chiles, marjoram, chopped cilantro, and water.
Check seasoning and add 1 pinch of salt to taste, if needed. Cover and simmer over low heat, stirring occasionally, until the meat is tender, about 1 hour. Skim excess fat off the stew before serving in bowls, garnished with a dollop of sour cream and a cilantro sprig on each bowl.
Working in batches, add mulato, ancho, and pasilla chiles, and cook, turning once, until toasted, about 2 minutes.
Transfer all chiles to a large bowl; pour over 5 cups boiling water and let sit until chiles are soft, about 30 minutes.
Drain, reserving soaking liquid, and remove stems and seeds from chiles, reserving 1 tsp. seeds from chiles.
Set seeds aside, and transfer chiles to a food processor; add 1 cup soaking liquid, and process until smooth.
Set chile purée and remaining soaking liquid aside.
Bring chicken and 8 cups water to a boil in a 4-qt. saucepan over high heat, reduce heat to medium-low, and cook until tender, about 45 minutes. Drain; set aside.
Meanwhile, arrange an oven rack 4" from broiler element, and heat broiler to high. Place garlic, tomato, tomatillo, and onion on a foil-lined baking sheet, and broil, turning as needed, until all vegetables are charred all over, about 15 minutes.
Transfer vegetables to food processor, and process until smooth.