Heat the olive oil in a large pot or Dutch oven over medium heat. Add the chopped onion and sauté for 5 minutes, or until the onion is translucent.
Add the minced garlic and sauté for an additional 1 minute, until fragrant.
Add the turkey necks to the pot and pour in the chicken broth or water. Bring to a boil.
Once boiling, reduce the heat to low and cover the pot. Let it simmer for 30 minutes to allow the flavors to meld.
After 30 minutes, add the chopped collard greens to the pot, stirring gently to combine.
Season with salt, black pepper, and cayenne pepper, if using. Stir well and cover again.
Simmer for an additional 1 hour, until the collard greens are tender and the turkey necks are cooked through.
If desired, stir in the apple cider vinegar right before serving to add brightness to the dish.
Serve hot, garnished with additional vinegar if you like.