In the bottom of your large slow-cooker put the carrots, celery, onion, potatoes and bay leaf.
Rinse the corned beef and place it on top of the vegetables, fat side up.
Pour the bottle of stout over the mixture.
Mix the brown sugar and red pepper flakes into the 1 cup of water and add to the corned beef. Then add the corned beef spices.
Put in enough water to cover the vegetables by at least one inch.
Cover the slow-cooker and turn to LOW.
Cook for 8 to 9 hours.
When the meat is tender, remove the meat and vegetables and cover with foil to keep warm.
Cut the cabbage into 6 wedges and add to the liquid in the pot.
Turn the heat to HIGH and cook until cabbage is crisp/tender, about 25-30 minutes.
Slice the meat across the grain and serve with the vegetables, whole grain mustard, ketchup and horseradish.
You can also serve with the extra cooking liquid.