In a large saucepot over high heat, bring the wine, and the aromatics from bay leaves down through peppercorns to a boil, cooking for about 3 minutes. Remove from the heat and let cool to room temperature. Whisk in the vinegar.
Place the wild boar leg in a baking dish or roasting pan. Pour the cooled marinade over it, and keep it in the refrigerator, loosely covered, at least overnight, but up to 36 hours, turning it at least four times.
Preheat the oven to 450°F.
Remove the boar from the marinade. Reserve 1 cup of marinade, and discard the rest. Pat the leg dry with paper towels. Score any fatty areas lightly with a sharp knife, using care not to cut into the meat.
Toss the twelve halved cloves of garlic with the fennel pollen. Make 24 slits all over the boar leg, and push a half clove of garlic and a bit of fennel pollen into each slit. Rub or brush the entire leg with a very light coating of olive oil, and season all over with salt and pepper.
Dry out the baking dish or roasting pan, return the leg to it, and slide it into the middle rack of the preheated 450°F oven, cooking it at high heat for 25 minutes.
Reduce the heat to 250°F and continue cooking until the internal temperature of the boar reaches 150°F. For a 6 pound leg this is likely to take 4-5 hours; a 10 pound leg can take 8 or more hours.
Remove the boar from the roasting pan, tent it with foil, and let it rest for at least 20 minutes.
Place your roasting pan on the stovetop over a burner at medium-high, and add the cup of reserved marinade and a fresh rosemary sprig to the roasting pan. Scrape the bottom of the pan with a wood spatula to free up the flavorful fond that’s adhering there.
Simmer until the wine reduces in volume by half. Sprinkle 1 tbsp of flour over the wine and whisk vigorously to incorporate it.
Add 2 cups of stock and the sour cherry preserves, continuing to whisk constantly to keep the flour from clumping, until the pan gravy reduces and becomes smooth and satiny, 8-10 minutes. Remove from the heat.
Thinly slice the wild boar from the bone and tile it on a platter. Pour the sauce over the meat, or serve it on the side.