01 -
Place quartered onion, smashed garlic, mustard seeds, peppercorns, cloves, allspice berries, crushed red pepper flakes, coriander seeds, and bay leaves into the Instant Pot.
02 -
Lay the corned beef brisket fat side up over the aromatics in the Instant Pot, then pour in beef broth.
03 -
Secure the Instant Pot lid and set the valve to sealing. Select 'Pressure Cook' or 'Stew/Meat' setting and cook on high pressure for 75 minutes.
04 -
Allow a natural pressure release for 20 minutes, then carefully perform a quick release to release any remaining pressure.
05 -
Remove brisket and rub the top with spicy mustard. Place on a foil-lined baking sheet, fat side up. Position the oven rack 8 to 10 inches from the broiler and broil on low until the top is caramelized and browned, about 2 minutes. Watch closely to prevent burning.
06 -
Slice against the grain into thin slices before serving to maximize tenderness.