Rinse the corned beef under cold water to remove excess salt.
Place the beef in the crockpot, fat side up.
Add the quartered onion and minced garlic around the beef.
Pour in the beef broth.
Sprinkle the black peppercorns and mustard seeds on top.
Add the bay leaf and brown sugar.
Arrange the chopped carrots and diced potatoes around the beef.
Cover the crockpot and set it to low for 8 hours or high for 4 hours.
Optional: Add cabbage wedges during the last hour of cooking.
Once done, remove the beef and let it rest before slicing.