Pre-Heat oven to 425°F.
Take the duck out of wrapping, pat dry and with a sharp knife, remove all excess fat from the neck and legs.
Transfer the duck to your wire rack, then in the roaster.
Cook for 45 minutes, or until golden.
Remove from oven and turn heat down to 275°F.
In a small bowl, mix together the Mustard, Apple Cider Vinegar, maple syrup and a good amount of salt and pepper.
Spread the mustard sauce all over the duck, covering all the fat of the duck.
Cover the duck with aluminum foil and return to oven for another 3 hours.
During that time, mix together the diced sweet potatoes, olive oil, cranberries and a good amount of salt and pepper.
Transfer to the roaster so it cooks with the duck when the duck has 30 minutes left.
Let the duck rest, uncovered for 15 minutes before carving and serving.
Add a generous amout of taragon all over the dish right before serving.