Rinse the corned beef and place in the bottom of a slow cooker. Add the bottle of stout, spices and enough water to just cover the meat. Cover and cook on LOW for six hours.
After six hours, add potatoes, carrots, onions, celery, and cabbage. If necessary, add a little more liquid to ALMOST cover vegetables, or shift the meat to bury vegetables in the hot liquid. Replace the lid and continue cooking for about 2 hours, or until cabbage is done to desired tenderness. (We like ours with a little crispness left in it.)
Remove beef after total cooking time of 8-9 hours. Allow to rest covered in foil for fifteen minutes. Slice brisket or round across the grain, serve with vegetables, mustard and horseradish sauce. Pass extra cooking liquid at the table.