01 - In a large pot, combine chicken broth, water, ham hock, onion, garlic, salt, black pepper, sugar, and red pepper flakes. Bring to a boil over medium-high heat.
02 - Reduce heat to low and simmer for 30 minutes to develop flavor.
03 - Add collard greens a few handfuls at a time, stirring until wilted before adding more.
04 - Cover and simmer on low heat for 1 to 1½ hours, stirring occasionally, until greens are very tender.
05 - Remove the ham hock, shred the meat, and return it to the pot if desired.
06 - Stir in apple cider vinegar and adjust seasoning to taste.
07 - Serve hot with some of the flavorful broth ("pot liquor").