Broil the tomatillos, poblanos and jalapeño 4 inches from the heat for 8 to 10 minutes until blistered and browned in spots.
Blend the roasted vegetables with the onion, garlic and broth until mostly smooth.
Season the pork with the salt, heat the oil in a Dutch oven over medium-high heat, and brown the pork in 2 batches for 5 minutes per batch.
Return all the pork, stir in the cumin and green sauce, and simmer partly covered for 90 minutes until the pork reaches at least 145°F and is fork-tender.
Simmer uncovered for 10 minutes until the sauce coats each pork cube.