Place the meat: Add your corned beef brisket to the slow cooker, fat-side up.
Add veggies: Place sliced onions, halved potatoes, and optional carrots around the meat.
Pour liquid: Add chicken stock and enough water to cover the brisket.
Season: Sprinkle in sea salt, cracked black pepper, and garlic.
Cook low and slow: Set your Crock Pot to low for 10 hours or high for 6 hours.
Add cabbage: About 2 hours before serving, add the chopped cabbage on top so it steams gently.
Serve: Slice the corned beef against the grain, plate with tender potatoes and cabbage, and drizzle with a little cooking broth. Serve with mustard or horseradish on the side.