Slow Cooker Corned Beef and Cabbage

Prepare the Corned Beef - Trim most of the visible fat from the corned beef, leaving about a ⅛ inch layer on top, or remove completely. Place it in a 6-quart slow cooker, fat side up. Sprinkle with pickling spice.
Add the Vegetables - Add the celery, carrots, onion, potatoes, garlic, and bay leaves along the sides and top. Add beef broth to the pot.
Slow Cook - Cover and cook until the corned beef and vegetables are tender, 4 to 5 hours on high or 8 to 9 hours on low setting.
Add the Cabbage - Arrange the cabbage on top of the corned beef, cover, and continue cooking until cabbage is tender, 30 to 60 minutes on high.
Make the Mustard Sauce - In a small bowl, mix together mustard, beer, and honey. Cover and refrigerate.
Check for Doneness - The meat is done when a fork can easily pierce it, and the internal temperature reaches at least 160ºF (71ºC). Remove the beef from the pot, and trim off any excess fat if desired.
Glaze with Sauce - Spread a thin layer of mustard sauce over the corned beef.
Optional: For a browned crust, place the meat on a foil-lined baking sheet and broil in the oven about 6 inches away from the top heating element. Cook until the mustard is lightly browned, about 5 to 8 minutes. Check every minute to monitor the browning to prevent burning.
To Serve - Slice the corned beef against the grain and serve with vegetables and extra mustard sauce.