01 - Rinse the corned beef under cold water to remove excess brine. Place it fat side up in the slow cooker.
02 - Sprinkle the contents of the spice packet over the brisket. Add mustard if using.
03 - Arrange onion, garlic, carrots, potatoes, bay leaves, and peppercorns around and on top of the meat.
04 - Pour beef broth and water over the ingredients.
05 - Cover and cook on LOW for 8 hours, or until the meat is fork-tender.
06 - Add cabbage wedges during the last 2 hours of cooking.
07 - Carefully remove the corned beef and let it rest for 10 minutes. Slice against the grain.
08 - Serve the corned beef with vegetables, spooning some broth over for extra flavor.