To prepare the greens: cut away the tough stalks and stems from the collards, and discard any leaves that are bruised or yellow. Fill the sink with water and salt (the salt helps to remove any impurities). Wash the collards thoroughly to remove the grit, 2 or 3 times, until the water runs clear. Dry thoroughly. Stack up several leaves and hand shred them into ribbon-like pieces (chiffonade). Repeat until all the leaves are shredded.
Coat a 6-quart stockpot with olive oil and place over medium heat. Add the onion and garlic, stir to coat, then add the ham hocks and bay leaves; cook about 8 minutes. Pack in the greens, pushing them down into the pot. Add the broth, vinegar, sugar, and red pepper flakes.
Bring up to a hard boil for 10 minutes, until greens start to wilt. Turn the greens over with a wooden spoon, do not stir. Lower to a gentle boil, cover the pot, and let cook for 45 minutes. Taste the "pot liquor" (broth) and check the seasoning, add seasoned salt. Cover and let cook for 15 more minutes.