Step 1: Boil tomatillos and jalapeños until soft.
Step 2: Blend with cilantro, onion, cumin seeds, garlic, and 1 cup of water to make the sauce.
Step 3: Boil pork ribs with salt, garlic, and bay leaf until tender.
Step 4: Strain and reserve 1.5 cups of cooking water.
Step 5: Simmer ribs with tomatillo sauce, potatoes, and reserved cooking water until potatoes are tender, then serve.