In a large Dutch oven or heavy-bottomed soup pot over medium-high heat, melt the butter. Add the onions, season generously with salt and pepper, and cook until softened, about 5 minutes.
Stir in the garlic, tomato paste, mustard powder crushed red pepper, cayenne, and paprika, and cook for 1 minute.
Add the ham hock and water and bring to a boil. Adding more water will result in more pot liquor, which some people simply can’t get enough of!
Add the greens a handful at a time, pushing them down with a wooden spoon to help them wilt into the liquid. When all the greens are in the pot, reduce the heat to a simmer and cook, partially covered, until the greens are very tender, 1 to 1 1/2 hours.
Taste the broth adjust seasoning as needed, then stir in the vinegar.
Serve immediately. The cooked greens will keep, refrigerated in their liquid, for up to 3 days. Reheat before serving.