Remove corned beef from package and rinse thoroughly to remove excess salt and brine.
Place in the Instant Pot on the steamer rack, fat side up. Rub the seasoning packet on the top and place crushed garlic cloves on top.
Place the garlic cloves, bay leaf and crushed red pepper on the corned beef. Pour the beer and stock over the top.
Pressure cook on high for 90 minutes. Let the pressure release naturally for 15 minutes then use the quick release to release any remaining pressure.
Remove from Instant Pot, let cool for 10-15 minutes then slice.
While your beef is cooling, strain the liquid to remove the peppercorns and seasoning and place it back in the Instant Pot.
Place the cabbage, carrots, and potatoes in the Instant Pot and pressure cook on high for 5 minutes.
Use the quick release to release the pressure. Place the vegetables and sliced corned beef on a plate, drizzle it with some of the cooking liquid, and serve with whole grain mustard.
Use a flat cut corned beef brisket for the best results. However, if you can't find flat cut, point cut will work as well.
Letting the pressure release naturally helps the meat to stay tender. Be patient.
Make sure to slice the corned beef against the grain so it stays tender.
If your corned beef doesn't come with a spice packet, make your ownCorned Beef Spice Packet with this recipe from Hilda's Kitchen Blog (use 2 tablespoons). You can also substitute 2 tablespoons of pickling spice.