About one hour. Pierce with a fork to test for doneness. When cool, remove meat from the bone and chop, if desired or leave whole. Pick through the greens removing yellow, wilted greens and large tough stems and veins. Fill the sink with cool water and wash the greens in three changes of water.
Fresh greens hold soil and dirt.
Swishing the greens through the cold water removes the clinging grit. While the greens drain, place a large Dutch oven over medium heat. Add the olive oil. When the oil is hot, not smoking, add the garlic, red pepper flakes and chopped onions. Stir and cook for about 30 seconds.