Pour the red wine into a small saucepan and simmer until reduced by two-thirds; set aside. Heat the duck fat in a large Dutch oven over high heat. Add the bones in a single layer and roast on all sides until browned, 6 to 8 minutes. Add the mushrooms, onion, shallot, carrot, and celery. Reduce the heat to medium-high and cook, stirring, until the vegetables are golden brown. Add the whisky and, with a wooden spoon, scrape the pan to loosen any browned bits from the bottom; reduce by half. Add the reduced wine, the chicken stock, and the peppercorns and simmer lightly for 1 hour, skimming as needed. Strain the liquid through a fine-meshed sieve into a large saucepan. Continue simmering the sauce to reduce by three-quarters, about 30 minutes, until it coats the back of a spoon. Add the vinegar and season with salt and pepper. Reserve, chilled.