- 1 cup kosher salt
- 1/2 cup (packed) light brown sugar
- 2 tablespoons black peppercorns
- 2 tablespoons coriander seeds, lightly crushed
- 2 tablespoons mustard seeds
- 12 thyme sprigs
- 2 bay leaves
- 4 cups apple cider, divided
- 1 (5-pound) boneless pork loin (tied if desired)
- 1 teaspoon kosher salt
- 1/2 teaspoon freshly ground black pepper
- 2 tablespoons vegetable oil
- 1/2 cup country Dijon mustard
- 1/3 cup (packed) light brown sugar
- 2 tablespoons maple syrup
- 2 tablespoons thyme leaves
- 2 cups apple cider
- Bring salt, brown sugar, peppercorns, coriander seeds, mustard seeds, thyme, bay leaves, 2 cups apple cider, and 2 cups water to a low boil in a medium saucepan over medium heat. Cook, whisking, until sugar and salt dissolve, about 4 minutes. Transfer brine to a large bowl and add remaining 2 cups apple cider and 2 cups ice. Let cool to room temperature.
- Place pork and brine in a large resealable plastic bag; turn to coat. Seal and chill at least 8 hours.
- Remove pork from brine and pat dry with paper towels. Let sit at room temperature 1 hour.
- Place rack in lower third of oven; preheat to 400°F.
- Season pork all over with salt and pepper. Heat oil in a large skillet over medium-high. Sear pork, turning occasionally, until browned on all sides (including ends), 10–12 minutes.
- Meanwhile, combine mustard, brown sugar, syrup, and thyme in a medium bowl.
- Pour apple cider into a large roasting pan or glass baking dish. Transfer pork, fat side up, to pan. Brush all over with mustard mixture. Roast pork, basting every 15 minutes, until an instant-read thermometer inserted into the center registers 140°F, 50–70 minutes.
- Transfer to a cutting board and let rest at least 15 minutes before slicing.
- Pork can be brined up to 24 hours ahead. Keep chilled in plastic bag.