Spread the dried black-eyed peas on a large baking sheet and remove any stones or damaged peas. Rinse thoroughly under cold running water.

Place the rinsed peas in a large pot and cover with water by 2 inches. Bring to a boil for 2 minutes, then remove from heat. Cover and let stand for 1 hour. Drain and rinse.

In a large Dutch oven or heavy-bottomed pot, add the ham hocks and heat over medium-high. Add the diced onion and sauté until translucent, about 5 minutes. Add the minced garlic and cook for 30 seconds until fragrant.

Add the soaked (or unsoaked) black-eyed peas, bay leaves, cumin, thyme, and red pepper flakes. Pour in the chicken broth or water and apple cider vinegar. The liquid should cover the peas by about an inch.

Bring the mixture to a boil, then reduce heat to maintain a gentle simmer. Cover and cook for 3-4 hours, until the peas are tender but not mushy. Check occasionally and add more liquid if needed.

When the peas are tender, remove the ham hocks. When cool enough to handle, remove the meat from the bones, chop it, and return it to the pot. Discard the bones and bay leaves.

Add the butter if using, and stir until melted. Season with salt and pepper to taste. The liquid should be thick and flavorful. If too watery, simmer uncovered for 10-15 more minutes.

Ladle the hot black-eyed peas into bowls, garnish with fresh parsley, and serve with cornbread or over rice.