Preheat the oven to 250°. Toss the sliced sausage with the mustard. Once slices are all coated, toss with the BBQ rub.
Put coated sausage in a baking dish, cover with foil, and bake for an hour.
Raise the oven temperature to 400°. Carefully pour the excess fat off of the sausage. Add the sauce and brown sugar to the sausage in the baking dish and combine well.
Bake uncovered for another 20 minutes or until some of the pointed edges are getting black.