In a stock pot on medium heat, melt the butter and then add the oil, onions, and ham hock. Stir and cook until the onions are translucent and tender. Add the garlic and cook a bit more, and then add the greens and saute until they become bright green. Add the stock, water, and vinegar, and then raise the heat to a boil, lower to a simmer, and cook for at least 1 1/2 hours. When ready, the ham hock meat will be easy to remove from the bone. Do so and make sure each serving gets a chunk of ham hock. Season with salt and pepper, to taste, remembering the ham hock and broth will add salt content. Add a little extra vinegar at the end, if desired.