Lay sliced onion on the bottom of the Instant Pot.

Scatter minced garlic and bay leaves on top of the onion.

Open the corned beef brisket package and place the beef into the Instant Pot, fatty side down.

Rub the pickling spice (or spice packed received with corned beef) onto the top of the brisket.  

Add the water and Guinness to the bottom of the pot.

Secure the lid of the Instant Pot, turn the sealing knob to SEALING.

Select PRESSURE COOK on HIGH for 1 hour and 30 minutes (90 minutes). It will take about 15 minutes for the pressure to build. 

When finished, press CANCEL. Carefully move the sealing knob to VENTING. Allow the pressure to release, this may take about 15 minutes.  

Use tongs and a spatula to remove the meat and onions from the Instant Pot and place it onto a plate. Tent with foil.

Discard about 1/2 the remaining liquid from the Instant Pot and add the cabbage, potatoes, carrots, and butter.

Place the lid back onto the pressure cooker, turn the sealing knob to SEALING, select PRESSURE COOK on HIGH for 3 minutes.  Press CANCEL, manually release the pressure, and carefully unscrew the lid.  

On a serving plate, cut the corned beef against the grain.  Add the vegetables to the plate and serve immediately!