For the crown roast: Mix the garlic and rosemary with the mustard and olive oil in a small bowl. Rub the pork with the mixture and marinate overnight.
The next day, rub the excess marinade off the pork. Tie both ends of the rack together by the bones to create a circle or "crown." Put the rosemary and sage sprigs on a sheet tray, and place the pork crown on top of the herbs.
Preheat the oven to 425 degrees F.
For the Italian sausage and cornbread stuffing: Heat the olive oil over a medium-high flame in a large Dutch oven until hot. Brown the sausage, then add the carrots, celery and onions. Cook over a medium flame, stirring constantly. Season with salt and pepper. When the vegetables are lightly browned, add the nutmeg and allspice and cook for 1 more minute. Add the cornbread and scallions, followed by the apples, currants and sage. Moisten the stuffing with the chicken stock as needed, just until it is moist but not mushy or falling apart. Season with salt and pepper.
Season the rack with salt and pepper. Stuff the stuffing into the center until the filling comes to the point of the meat meeting the bone. Roast until caramelized, 15 minutes. Reduce the heat to 350 degrees F and cook until the center of the pork registers 155 degrees F, another 2 hours.
For the dijonnaise: Meanwhile, heat the cream in a saucepan over medium heat until reduced by half. Whisk in the apples, mustard and sage. Season with salt and pepper.
Set the meat aside to rest for at least 10 minutes, and spoon the stuffing into a bowl. Slice the meat and serve with the dijonnaise.