Heat oven according to the directions on the ham package. Place the ham on a rack in a roasting pan and pour the ginger ale over the top. Cover the pan with foil and bake according to the package directions.
Meanwhile, in a small bowl, combine the brown sugar and mustard. About 20 minutes before the ham is finished, remove the foil and spoon the mustard mixture over the ham. Continue to bake, uncovered.
Meanwhile, place the potatoes in a large pot with enough water to cover them. Add 2 teaspoons of the salt and bring to a boil. Simmer until tender, about 15 minutes. Drain, then return the potatoes to pot. Add the butter, sour cream, Cheddar, pepper, and the remaining salt to the potatoes and roughly mash. Cover to keep warm until the ham is done.
Slice the ham, spoon the pan juices over it, and serve with the potatoes. Sprinkle with the parsley, if desired.
Tip: Use a slightly larger ham (2 to 3 pounds) and enjoy plenty of leftovers.