Trim and discard fat from pork; cut pork into 1-inch cubes.
Heat oil in a wide 3 to 4 quart pan over medium-high heat. Add meat, a few pieces at a time, and cook until lightly browned on all sides. Lift out meat, transfer to a plate, and keep warm; reserve drippings in pan. Add onion to pan and cool, stirring, until soft (about 7 minutes). Return meat to pan and stir in garlic, tomatillos, chiles, marjoram, chopped cilantro, and water. Season to taste with salt. Cover and simmer until meat is tender when pierced (about 1 hour). Skim off fat.
Spoon into serving bowls and garnish with sour cream and cilantro sprigs.