To prepare the kale, cut away the stalks and thick vein along center of the leaves. Discard any leaves that are bruised or yellow. Fill the sink with water and a palmful of kosher salt (the salt helps remove any impurities) and wash the kale thoroughly to remove any grit that may be trapped in the curly leaves. Repeat this washing process at least two or three times or until there is no grit left on the bottom of the sink; drain the kale completely and pat dry with a paper towel.

Stack the kale leaves a few at a time; cut the kale crosswise into ribbons.

Heat the oil in a large, deep pot over medium heat. Add the onion and garlic, stir to coat, then add the ham hocks and bay leaves; cook for about 10 minutes, or until the onions are softened.

Pack in the greens, pushing them down into the pot; then add the low-sodium stock, apple cider vinegar, sugar, and red pepper flakes.

Bring the mixture to a rolling boil and cook for 10 minutes, until the greens start to wilt, then turn the greens over with a wooden spoon and lower the heat until the liquid is simmering. Cover; cook for 45 minutes. Taste the broth and add kosher salt as need. Cook, covered, for an additional 10 minutes. Remove the bay leaves. Serve hot. Makes 8 to 10 servings plus leftovers.