Place the trotters, whole heads of garlic, bay leaves, thyme, cider and Calvados, if using, in a pot. Bring up to the boil, and reduce to a simmer. After 2 hours add the tripe. Cook for approximately another 1–1½ hours, until the tripe and trotters are cooked: when you pinch them, your fingers easily go through the flesh. Remove the tripe, trotters, herbs and garlic from the liquor, which you should leave cooking to reduce by half. Pull the flesh off the trotters while still warm and add to the tripe, discarding the bones.