Instant Pot Corned Beef and Cabbage

Name: Instant Pot Corned Beef and Cabbage
Ingredients: 1 teaspoon mustard seeds; 1 teaspoon black peppercorns; ½ teaspoon juniper berries (about 12); ¼ teaspoon allspice berries (about 6); 2 dried bay leaves; 1 flat-cut corned beef brisket (3 to 4 pounds), trimmed of excess fat; 1 yellow onion, peeled and quartered; 3 cloves garlic, smashed and peeled; 1 ½ pounds carrots, peeled and cut into 3-inch pieces; 1 ½ pounds small red potatoes; ½ head green cabbage (1 ½ pounds), quartered lengthwise; Whole-grain mustard, for serving