Wash collard greens thoroughly in 2–3 changes of water to remove grit.
Optional: blanch greens in boiling water for 2 minutes, then drain.
In a large pot, cook bacon or sear smoked meat. Leave about 2 tablespoons of fat in the pot.
Add onion and cook 6–8 minutes until soft and lightly golden. Stir in garlic and cook 30 seconds.
Add chicken broth, smoked meat, black pepper, red pepper flakes, and ¼ tsp salt. Simmer 10–15 minutes.
Add greens in batches, stirring as they wilt down.
Reduce heat to low and simmer gently (do not boil) for 45–90 minutes, until greens are tender.
Uncover and cook 10–15 minutes to slightly reduce the liquid.
Stir in apple cider vinegar, remaining salt to taste, and sugar if needed.
Remove meat, shred, and return to pot. Let rest 10–15 minutes before serving.