For serving: grainy mustard and horseradish sauce, recipe below
Place celery, carrots, onion and potatoes in the bottom of a large slow-cooker or crock pot. Rinse the corned beef brisket and place over vegetables. Add the bottle of stout, spices and enough water to just cover the meat. Cover and cook on LOW for eight to nine hours.
Remove the meat and vegetables from the pot and cover with foil to keep warm. Increase heat to high and cook cabbage until softened but still crispy, 20 to 30 minutes.
Slice brisket across the grain, serve with vegetables, mustard and horseradish sauce. Pass extra cooking liquid at the table.
Whip cream to soft peaks and then fold in sour cream and horseradish, to taste. Season with salt, pepper and a dash of hot sauce.;