Rinse a corned beef brisket under cold water
Place the brisket in the slow cooker, fat side up
Add the seasoning packet that came with the meat
Add enough water, broth, or a mix of both to cover the brisket halfway
Add optional aromatics such as onion, garlic, bay leaves, peppercorns, or mustard seeds
Cover and cook on low for 8 to 10 hours, or until tender
Add carrots, potatoes, and cabbage during the last 2 to 3 hours of cooking if desired
Check that the meat is fork-tender before removing it
Transfer the corned beef to a cutting board and let it rest for 10 to 15 minutes
Slice the corned beef against the grain
Serve with the cooked vegetables and some cooking liquid if desired