In a large Dutch oven, add the bacon to the pan over medium heat and cook until the fat begins to render. When the bacon is almost crisp, add the onions and sweat for 3 minutes. Add the garlic and sweat for an additional minute. Remove the tough stems of the greens and discard. Roughly chop the greens and tender stems and add them to the pan with the chile flakes and a large pinch of salt. Cover and cook over low heat for 10 minutes. Remove the lid and add the vinegar and sugar. Put the lid back on and cook for an additional 30 minutes. Remove from the heat and check your seasoning; if it's not spicy enough for you, add your favorite hot sauce to taste.
Recipe courtesy of Michael Symon