Fill a large stockpot with 1 quart of water.
Add ham hock, bring to a boil, then reduce heat to low and simmer, covered, for 1 hour.
In the meantime, remove the stems from the greens. Discard the stems and coarsely chop the leaves.
Remove the ham hock from the pot and set aside to cool.
Add the greens, bacon grease, cider vinegar and sugar to the pot.
Cook, uncovered, for 2 hours for firmer greens, longer for more tender greens. My experience is, the longer they cook the better they taste.
Remove any meat from the ham hock or bone. If using bacon, chop the bacon up. Add the meat back to the pot and stir.
Season greens with salt and pepper.