Suzanne Goin's Corned Beef and Cabbage with Parsley-Mustard Sauce

INGREDIENTS

• 2 onions
• 1/4 cup red wine vinegar
• 3/4 cup chopped flat-leaf parsley
• 1/4 cup plus 2 tablespoons finely diced shallots
• 1/2 bunch thyme
• 9 golf ball-sized turnips
• 1/2 lemon, for juicing
• 1 6-pound corned-beef brisket
• 2 bay leaves, preferably fresh
• 4 whole cloves
• 1 medium green cabbage (about 2 pounds)
• 1/2 cup plus 2 tablespoons extra-virgin olive oil
• 1 tablespoon whole grain mustard
• 2 chiles de arbol
• 1 1/4 pound yellow potatoes, peeled
• 6 small carrots
• Kosher salt and freshly ground black pepper