Place corned beef brisket in inner pot and sprinkle the beef seasoning packet over the meat.
Pour in Guinness and beef broth around corned beef.
Close and lock the lid.
Turn the pressure release valve to sealing.
Press manual high pressure and adjust the time to 85 minutes.
When the cooking time is finished, let the pressure release naturally for 20 minutes.
Carefully turn the pressure release valve to venting to release the remaining pressure.
Unlock and remove the lid.
Remove the brisket to a plate and tent with foil to keep warm. Do not drain inner pot.
Add the potatoes, carrots, and cabbage to the inner pot.
Close and lock the lid.
Turn the pressure release valve to sealing.
Press manual high pressure and adjust the time to 3 minutes.
When the cooking time is finished, allow the pressure to release naturally.
Unlock and remove the lid.
Remove the vegetables.
Drizzle the melted butter over the vegetables and season with salt and pepper.
Slice the corned beef into thin slices, slicing against the grain.
Notes
Spice packet: To make your own spice packet, combine, 1 teaspoon each: yellow mustard seeds, whole black peppercorns, and coriander seeds, ½ teaspoon whole allspice, 3 whole cloves, and 2 bay leaves.
Beef broth: I recommend using reduced-sodium beef broth to better control the amount of salt in this recipe.