Preheat the oven to 300°F. Strain and reserve the liquid from the marinated ingredients and pat them dry. Separate the bacon and legs from the vegetables and sachet. Season the legs with salt and pepper on all sides. Place a large heavy-bottomed Dutch oven over medium heat and add the duck fat and bacon. Cook, stirring, until the bacon is browned, 4 to 5 minutes, then remove with a slotted spoon and set aside. Add the hare legs and sear on all sides until golden brown, 8 to 10 minutes; remove and set aside. Add the bones in a single layer (you may need to do this in batches). Roast on all sides until browned, 10 to 12 minutes. Remove the bones, set aside, and reduce the heat to medium. Add the marinated vegetables and sachet to the pot. Cook, stirring, for 5 minutes. Add the reserved marinating liquid to the pot, bring to a simmer, and reduce by half, about 20 minutes. Return the bacon, hare legs, and bones to the pot and stir in the veal stock. Bring to a simmer, cover, and transfer to the oven. Braise for 2 to 2½ hours, until the leg meat easily separates from the bones. Remove the legs from the liquid, transfer to a baking dish, cover with plastic wrap, and reserve in a warm spot. Strain the braising liquid through a fine-meshed sieve into a large saucepan and discard the solids. Bring to a simmer and reduce, occasionally skimming away any foam that rises to the surface, for 2 hours, or until it is thick enough to coat the back of a spoon. Reserve the sauce, chilled.