Rinse the corned beef under cold water to remove excess brine.
Place the brisket in the crockpot, fat side up.
Add the quartered onion and minced garlic around the meat.
Pour in the beef broth, covering the brisket halfway.
Sprinkle mustard seeds and black peppercorns over the meat.
Add carrots and potatoes around the brisket.
Cover and cook on low for 8 hours or high for 4 hours.
In the last hour of cooking, add cabbage wedges on top.
Once done, remove the brisket and let it rest for 10 minutes before slicing.
Serve with vegetables and garnish with fresh parsley.