Cider-Brined Pork Roast with Potatoes and Onions

Bring brown sugar, 1 cup salt, 2 bay leaves, 1 tablespoon coriander seeds, 1 teaspoon peppercorns, and 2 cups water to a boil in a medium saucepan. Reduce heat and simmer, stirring occasionally, until sugar and salt dissolve, about 4 minutes. Transfer brine to a large bowl and add cider and 2 cups ice. Let cool. Place pork and brine in a large (2-gallon) resealable plastic bag. Seal bag and chill at least 8 hours. Remove pork from brine and pat dry with paper towels. Let sit at room temperature 1 hour. Toss potatoes and onions with 4 tablespoons oil in a large roasting pan or on a large rimmed baking sheet; season with salt and pepper and set aside. Place rack in lower third of oven and preheat to 425 °F. Using the side of a chef's knife, crush remaining 2 tablespoons coriander seeds. Season pork with salt and pepper and rub all over with crushed coriander. Heat remaining 1 tablespoon oil in a large skillet over medium-high heat. Cook pork until browned on all sides, 8 –10 minutes. Transfer pork to roasting pan and nestle in among vegetables. Tuck remaining 6 bay leaves under kitchen twine over top of pork. Wrap bone tips with foil to prevent burning and roast, turning vegetables halfway through, until an instant-read thermometer inserted in the center of pork registers 140 °F, 60 –75 minutes. Remove foil from bones and transfer pork to a cutting board; let rest 30 minutes before slicing between ribs into chops. DO AHEAD: The pork can be brined 2 days ahead. Keep chilled.