Add any juices from the beef, beer, onion, and garlic to the bottom of a 6 quart Instant Pot.
Rub the corned beef with the spice mixture (or pickling spice) and place on the trivet in the Instant Pot.
Set Instant Pot to high pressure and cook for 90 minutes. Once time is up, allow natural release for 15 minutes, then manually release pressure. Remove corned beef, and place on a cutting board or serving tray. Loosely tent with foil to rest while preparing vegetables.
Leave about 1-1 ½ cups liquid in the Instant Pot. Place trivet in the bottom. Add broth, cabbage, potatoes, and carrots. Sprinkle with salt and pepper. Set to high pressure and cook for 5 minutes.
Quick-release pressure, and remove vegetables to a serving platter and cover to keep warm. To thicken the sauce, turn Instant Pot to saute. Mix cornstarch with equal parts water. While stirring the sauce, mix in the slurry until sauce thickens.
Slice cooked corned beef against the grain, and serve with vegetables and sauce.
Notes
*A dark beer, such as Guinness, may give a slightly more bitter flavor.
Nutritional information does not include optional gravy
Add a tablespoon of brown sugar to the sauce for a sweet contrast to the tart and briny flavor of the corned beef.
Refrigerate the veggies and the beef in separate containers for up to 4 days. Freeze cooled and sliced corned beef for up to 2 months in a labeled zippered bag or container.
Reheat portions in the microwave, on the stovetop or quickly in the Instant Pot!