Rinse the collard greens thoroughly
Remove the tough stems
Stack the leaves, roll them, and slice them into strips
Heat oil in a large pot over medium heat
Add chopped onion and cook until soft
Add minced garlic and cook briefly
Add vegetable broth or water
Add the collard greens to the pot
Stir in salt, black pepper, and red pepper flakes if desired
Add a splash of apple cider vinegar or lemon juice
Cover and simmer until tender
Stir occasionally and add more liquid if needed
Taste and adjust seasoning before serving