Place the chopped onion at the bottom of a 6-quart slow cooker.
Lay the corned beef brisket over the onions and sprinkle with the provided spice packet. If the brisket doesn’t include spices, use a mix of pickling spices, peppercorns, and a bay leaf.
Pour enough water into the slow cooker to almost cover the brisket. Add the garlic and bay leaves to the water.
Set your slow cooker to low and cook for 8-10 hours. The slower, longer cooking time helps achieve that ultra-tender texture.
Three hours into the cooking time, add the potatoes and carrots, making sure they’re fully submerged in the broth.
Two hours before serving, carefully nestle in the cabbage wedges on top of the other vegetables. Allow them to steam and soak up the flavorful broth.
Once finished, remove the corned beef and let it rest for 15 minutes to lock in the juices. Slice it against the grain for the most tender bites.
Serve the corned beef warm with a side of potatoes, carrots, and cabbage. Spoon some of the savory broth over everything for extra flavor.