Using your hands, pull the leaves from the thick collard greens stems, and discard the stems. Roll the leaves lengthwise into a cigar shape, and cut crosswise into large pieces. Fill a clean sink or a large pot with plenty of cold water, and rinse the greens in the water, allowing any dirt or grit to sink to the bottom (repeat several times with fresh water, if necessary). Lift the greens out of the water, and set aside in a colander to drain.

Heat the ham hocks, salt, and 3 cups water in a large pot over medium-high heat. Bring the water to a boil, reduce the heat to low, and simmer until the ham hocks are slightly tender, about 30 minutes. Add the greens, sugar, and red-pepper flakes to the pot, stirring to combine. Cover the pot, and continue cooking over low heat, stirring occasionally, until the greens are tender, about 45 minutes. If the pot gets too dry, add more water as necessary to keep the greens moist (you’ll want to serve the greens with a generous amount of the flavorful cooking liquid).