Preheat oven to 400F. Place parsley stems, rosemary, thyme, bay leaf, and black peppercorns in a piece of cheesecloth to make a bouquet garni. Tie with string and set aside.

Pat oxtail dry and season with salt and pepper. Place Dutch Oven over medium-high heat and add oil. Sear oxtail for 3–4 minutes per side, then remove from pan and set aside.

Add the onion, carrots, and fennel bulb. Using the rendered fat, sweat the aromatics until tender, 5–8 minutes. Stir in the tomato paste, then return the seared oxtails to the pan. Cook, stirring constantly, until the tomato paste turns slightly darker red.

Deglaze with red wine and let the liquid reduce by half. Add parsley leaves, beef stock, and balsamic vinegar, stirring to combine.

Cover with lid and place in the oven. Cook until the meat is tender, checking after about 60 minutes, for about 90 minutes total.

Season with salt and pepper to taste and garnish with reserved fennel fronds. Serve with potatoes, rice, polenta, or grits.