Rinse the corned beef brisket under cold running water. Pat dry with paper towels.
Add the sliced onions, garlic, pickling spices, beef broth and beer into the pressure cooker.
Place the trivet at the bottom of the pot and place the corned beef brisket on top, fat side up.
Close the lid and set the valve to “seal”. Pressure Cook on HIGH pressure for 85 minutes.
When done, let the pressure release naturally for 15 minutes then do a quick release to get rid of any remaining pressure.
Remove the meat from the pot and let it rest for about 10 minutes, loosely tented with aluminum foil.
While the meat is resting, strain the cooking liquid and discard the solids. Reserve 1 1/2 cups of the cooking liquid.
Pour the strained cooking liquid into the pot, add the potatoes, carrots and cabbage.
Close the lid and set the valve to “seal”. Pressure Cook on HIGH pressure for 3 to 4 minutes (depending on the size of your potatoes).
Do a quick release of pressure by setting the valve to "venting". Remove the vegetables from the pressure cooker.
Slice the brisket against the grain and serve with the vegetables.
OPTIONAL: Drizzle the vegetables with melted butter and serve with a side of whole grain mustard.