Place brisket on aluminum foil. Spread each side of the brisket with prepared mustard and whole mixed pickling spices. Wrap foil tightly around brisket and place in 8 x 10 baking dish. Bake in slow oven (225 degrees F.) 3 1/2 hours or until done. Remove brisket from foil. Scrape off and discard pickling spices from brisket and trim any excess fat. Cut brisket into 4 to 6 equal portions and place in 8 x 10 baking dish. Rinse and drain sauerkraut and place on top of brisket. Sprinkle with grated Swiss cheese. Place under the broiler until the cheese has browned, about 8 to 10 minutes. Garnish with prepared mustard.