Trim spareribs of excess fat and cut between bones into 1-1/2 to 2-inch cubes. Season with salt and pepper to taste.
In a pot over medium heat, heat about 2 tablespoons oil. Add pork ribs and cook, turning once or twice, until lightly browned on all sides. Cook in batches as needed.
Add cumin and continue to cook for about 1 to 2 minutes or until meat is coated. Remove meat from pan and keep warm.
Add onions and garlic and cook, scraping bottom and sides of the pan, until softened.
Return pork ribs to pot. Add 4 cups chili verde sauce and 1 cup water. Bring to a boil. Lower heat, cover, and cook for about 2 to 3 hours or until ribs are fork-tender. Add water in 1/2 cup increments if the sauce is drying out before the meat is fully tender.
Season with salt and pepper to taste. Serve hot with lime wedges and corn tortillas.
For the Chili Verde Sauce
On a foil-lined baking sheet, arrange tomatillos and garlic in a single layer. Broil for about 6 to 8 minutes or until skins are lightly charred. Peel garlic.
In a food processor or blender, combine tomatillos, garlic, jalapenos, and cilantro. Pulse a few times until coarsely smooth. Makes about 4 cups.