Combine onions, ham hocks, garlic and water in a large soup pot
Bring to a boil and simmer (covered) for 2 hours
Cut out collard green steams and discard, chop leaves into 1" strips
After mixture has simmered for 2 hours, add the collards, vinegar, sugar, salt, pepper and red pepper flakes and mix well
Simmer (covered) for another 2 hours
Serve warm
Nutrition Info Per Serving: Calories 95 Total Fat 1 g Cholesterol 0 mg Sodium 1137 mg Potassium 793 mg Total Carbohydrate 15g Dietary Fiber 5 g Sugars 5 g Protein 9 g