Season ribs generously with salt and pepper. Let ribs come to room temperature for 30 minutes. Pat dry with paper towel.

Heat oil in a large Dutch oven over medium-high heat. Brown ribs on all sides, working in batches to avoid crowding the pan, about 8 minutes per batch. Transfer browned ribs to a tray and set aside.

Preheat oven to 275°F.

Discard all but 2 tablespoons of the fat remaining in the pot. Adjust heat to medium and sauté the garlic until golden, about 2 minutes. Add onions, carrots, celery, ½ teaspoon salt, and ¼ teaspoon freshly ground black pepper. Continue sautéing, stirring frequently, about 10 minutes or until carrots are tender.

Stir in tomato paste and cook a few minutes until tomato paste has begun to caramelize, about 3 minutes. Sprinkle with flour and sauté another minute or two.

Slowly pour in the wine, scraping the bottom of the pot to loosen any browned bits. Simmer wine for a few minutes until reduced by about half. Add 2 cups beef stock, Worcestershire, thyme, and bay leaf to the pot. Stir to combine. Taste and adjust seasoning as needed.

Return the short ribs to the pot, making sure all the meat is covered by the liquid. Add more stock if needed to cover the meat. (It’s okay if the bones stick out a bit.) Bring to a simmer, cover with lid and place on center rack of preheated oven.

Cook in oven for 4 hours without opening lid.

If serving the next day (recommended)- Remove from oven and let cool to room temperature. Once cooled, remove bay leaf and thyme sprigs, then refrigerate overnight until 45 minutes before you plan to serve. Remove from refrigerator, lift solid fat layer from surface, then heat over medium heat for 30 minutes or until heated through and simmering. Add parsley and chives and adjust seasoning as needed. Serve hot with mashed potatoes.

If serving the same day- Remove from oven and transfer short ribs to a serving platter with tongs. Remove thyme sprigs and bay leaf. Skim off fat from sauce, then stir in parsley and chives. Taste and adjust seasoning as needed. Pour sauce over short ribs and serve with mashed potatoes. You could also serve directly from the Dutch oven, but it is more difficult to skim the fat from the sauce while the ribs are still in the pot.