Step 1

In a mortar and pestle, coarsely crush mustard seeds, peppercorns, juniper, allspice, and bay leaves (alternatively, place in a resealable bag and crush with a rolling pin). Add to the bowl of a multicooker, along with brisket, onion, and garlic. Add enough water to completely cover brisket, about 8 to 10 cups. Secure lid of multicooker. Cook on high "Pressure Cook" setting for 1 hour, 25 minutes. Once time is complete, turn off machine and manually release pressure; carefully remove lid. Using tongs, transfer brisket to a cutting board; tent with foil to keep warm.

Step 2

Add carrots, potatoes, and cabbage to bowl of multicooker. Secure lid, readjust pressure valve, and cook on high "Pressure Cook" setting for 5 minutes. Once time is complete, turn off machine and manually release pressure; carefully remove lid (do not let vegetables sit on the warming setting). Using a slotted spoon, transfer vegetables to a platter. Thinly slice brisket against the grain and transfer to platter. Spoon some of the cooking liquid over brisket and vegetables; serve with mustard.