1. In a 5- to 6-quart pan, combine tomatillos, onions, lima beans, garlic, chilies, and 3 1/2 cups water.
2. Bring to a boil over high heat; reduce heat, cover, and simmer until vegetables are tender when pierced, about 20 minutes. Drain, reserving cooking liquid.
3. Whirl vegetable mixture in a food processor or blender until smooth. (If desired, chill purée and liquid airtight up to 1 day.)
4. Return purée to pan. Cook, uncovered, over medium heat, stirring often, until purée is as thick as catsup, about 15 minutes.
5. With a fork, blend prepared masa with 1 cup reserved cooking liquid; add to purée.
6. Whirl fennel, cilantro, parsley, and epazote with broth in a food processor or blender; add mixture to cooked sauce. Heat just until hot.
7. Ladle 3/4 cup sauce onto each dinner plate; lay pork slices in sauce and garnish with parsley. Season with salt and pepper to taste. Accompany with remaining sauce.