Slice the onions and place them at the bottom of the slow cooker.

Add the corned beef (plus spice packet if it comes with one), fat side up so it melts into the meat while it's cooking.

Pour the kombucha in around the meat.

Cover and cook on low for 8 hours.

Remove the corned beef from the slow cooker, let it rest for 20 minutes. Slice it against the grain and serve on rye bread sandwiches. Strain the onions out of the juice and add to the sandwiches.

Put the remaining juice into a container and put in the fridge overnight. Remove the chilled fat layer the next day. You can use this liquid to braise your cabbage or carrots in to get amazing flavor!