adapted from the Joy of Cooking; serves 4–6
Place ham hock in a large dutch oven or heavy-bottomed soup pot and cover with water by a couple inches. Add the onions, carrots, celery, parsley, thyme, bay leaf, garlic, salt, and red chile flakes. Bring to boil, lower heat and cover leaving a steam gap. Simmer slowly for an hour, skimming the surface with a spoon to remove any "goo" that floats to the top.
While the broth cooks, prepare the greens: dunk in a big bowl of water, lift out to a clean towel, then remove the tough center ribs and stem. Stack and roll the leaves to slice (chiffonade) then give the mound a cross chop so you end up with 3- or 4-inch strips.
Since this is about the size of half a leaf, you can always cut the leaves in half first then chiffonade from there.
Add the greens and simmer for an additional 90 minutes to 2 hours, until meat is falling apart and tender.
Remove the bundle of parsley/thyme and discard. Separate the ham from bone and reserve, discard bone and remaining sinew. Pour off and reserve the cooking liquid for another use.
Season the greens (and what remains of the carrots and celery) with apple cider vinegar and pass additional salt, black pepper, and red chile flakes at the table along with the ham.