Cut the collards into 1- to 2-inch pieces, wash them in warm to hot water at least 2 or 3 times, then leave them in warm water until needed. Place all the meat in a large pot, 2/3 filled with water, cover then boil 20 to 30 minutes.
Drain the water and refill the pot; then cover and boil the meat again for about 1 hour.
Drain the collards; add them to the cooked meat and stock, along with the onion, and salt and pepper, to taste. Cook the whole potful for another 30 to 45 minutes. Some people like greens cooked less, so they're chewy. The longer you cook them, the more tender they get. Serve alone, over rice, grits or potatoes, or as a side dish.