In a large nonreactive pot, heat the oil over medium heat. Add the onion, carrot, and celery and cook until the vegetables are softened, about 6 minutes. Stir in the garlic, rosemary, thyme, peppercorns and orange zest. Add the wine and bring to a boil over high heat. Reduce the heat to low and simmer for 10 minutes. Cool the marinade completely. Place the short ribs in a large nonreactive bowl and add the cooled marinade. Cover and refrigerate at least overnight, preferably 24 hours.
Strain the marinade into a large nonreactive pot and discard the solids. Bring the marinade to a boil over high heat. Boil until reduced by one-fourth, 20 to 30 minutes. Preheat the oven to 325 degrees F. Place the short ribs in a large, flameproof nonreactive casserole (such as enameled cast iron). Add the reduced marinade and the veal stock. Bring to a boil over high heat. Cover and bake until the beef is very tender and pulling from the bones, 3 1/2 to 4 hours. Transfer the beef to a platter and cool. Discard the bones, trim away any excess fat, and return the beef to the casserole.
Meanwhile, skim off and discard the fat on the surface of the cooking liquid. Strain the sauce into a large nonreactive pot and bring to a boil over medium heat-high. Add the olives and anchovies. Cook, skimming often, until the sauce reduces and is thick enough to coat a wooden spoon, about 30 minutes. Pour the sauce over the short ribs. (The short ribs can be prepared up to 1 day in advance, cooled, covered, and refrigerated.) Assembly: Bring the short ribs and sauce to a simmer over medium heat and cook until the short ribs are heated through, about 10 minutes. Spoon a portion of the potato pure onto the centers of 8 warmed dinner plates, and top each with the short ribs. Spoon the sauce around the potatoes.
Place the potatoes in a large pot, add enough cold water to cover by 2 inches, and bring to a boil over high heat. Add the 3 tablespoons of salt and cook until the potatoes are tender when pierced with the tip of a sharp knife. Drain and rinse under cold water until easy to handle. Peel the warm potatoes. Pass the potatoes through a potato ricer into a large bowl. Beat in the butter, olive oil, horseradish, and optional cheese. Season with salt and pepper. (The potato pure can be made about 20 minutes ahead, placed in a heatproof bowl, loosely covered, and kept warm over a pot of simmering water