Place the tripe, water, quartered onion, crushed garlic, and bay leaves in a stockpot. Bring to a boil, skim, then simmer gently for 90 to 120 minutes until tender.
Lift out the tripe and cool slightly. Reserve 3 cups of cooking liquid, then cut the tripe into irregular bite-size pieces.
Make the Sauce:
Heat the achiote oil in a Dutch oven. Cook the chopped onion for 6 minutes, then add minced garlic, cumin, oregano, and salt for 30 seconds.
Blend the peanut butter with the milk and 1 cup reserved cooking liquid until smooth. Pour into the pot with the potatoes and remaining 2 cups cooking liquid.
Simmer for 15 minutes. Add the tripe and cook for 20 to 25 minutes until the potatoes are tender and the sauce lightly thickens.
Serve:
Toss the red onion with the lime juice and a pinch of salt. Let stand for 10 minutes.
Serve the guatita with white rice, avocado, and the quick-pickled onion.
Notes
Tripe cooking time varies; it should be tender but retain a gentle chew before it enters the sauce.
If the sauce thickens too much, loosen it with reserved tripe broth or milk.