Ingredients

• 1/2 medium onion, chopped
• 2 garlic cloves, peeled, crushed
• 1 bay leaf
• 1/2 cup kosher salt
• 1/4 cup (packed) light brown sugar
• 1 teaspoon coriander seeds
• 1 teaspoon fennel seeds
• 1 teaspoon black peppercorns
• 1 orange, halved
• 1 lemon, halved
• 4 sprigs thyme
• 1 5-pound center-cut bone-in pork loin, chine bone removed
• 1 tablespoon coriander seeds
• 1 tablespoon fennel seeds
• 1/4 cup (packed) light brown sugar
• 2 tablespoons kosher salt
• 1 tablespoon coarsely ground black pepper
• 1 tablespoon paprika
• Vegetable oil (for grilling)
• Peach Mustard ( for serving)
• Mortar and pestle or spice mill

Instructions

1. Bring onion, garlic, bay leaf, salt, brown sugar, coriander seeds, fennel seeds, peppercorns, and 2 cups water to a boil in a medium saucepan. Reduce heat and simmer, stirring, until salt and sugar are dissolved. Remove from heat and add 2 cups cold water. Transfer brine to a large heatproof bowl or jar. Squeeze orange and lemon juice into brine and add citrus halves and thyme. Chill until cool.
2. Place pork in a large resealable plastic bag and add brine. Seal bag, pressing out air, and chill at least 12 hours.
3. Do ahead: Brine can be made 2 days ahead; cover and keep chilled. Pork can be brined 24 hours ahead; keep chilled.
4. Dry Rub and Assembly: Remove pork from brine, brushing off any spices. Let stand at room temperature 1 hour before grilling. Toast coriander and fennel seeds in a small skillet over medium heat, tossing occasionally, until fragrant, about 2 minutes. Let cool, then finely grind in mortar and pestle or spice mill; combine in a small bowl with brown sugar, salt, pepper, and paprika. Prepare grill for 2-zone heat (for a charcoal grill, bank coals on 1 side of grill; for a gas grill, leave 1 or 2 burners off) and oil grate. Pat pork dry and rub all over with dry rub. Grill over direct heat, bone side up, until lightly charred, about 5 minutes. Turn pork and grill, bone side down, until lightly charred, about 5 minutes more. Transfer pork to cooler side of grill, bone side up; cover grill. Grill pork, turning occasionally, until an instant-read thermometer inserted into the center of loin registers 145°, 45–60 minutes. (The internal temperature of grill should be 400°; add more charcoal or adjust heat as needed.) Transfer pork to a cutting board, tent loosely with foil, and let rest 20 minutes. Cut loin from ribs, and slice loin; cut between ribs. Serve with Peach Mustard. Do ahead: Dry rub can be made 1 day ahead. Store airtight at room temperature.
5. Remove pork from brine, brushing off any spices. Let stand at room temperature 1 hour before grilling.
6. Toast coriander and fennel seeds in a small skillet over medium heat, tossing occasionally, until fragrant, about 2 minutes. Let cool, then finely grind in mortar and pestle or spice mill; combine in a small bowl with brown sugar, salt, pepper, and paprika.
7. Prepare grill for 2-zone heat (for a charcoal grill, bank coals on 1 side of grill; for a gas grill, leave 1 or 2 burners off) and oil grate. Pat pork dry and rub all over with dry rub. Grill over direct heat, bone side up, until lightly charred, about 5 minutes. Turn pork and grill, bone side down, until lightly charred, about 5 minutes more.
8. Transfer pork to cooler side of grill, bone side up; cover grill. Grill pork, turning occasionally, until an instant-read thermometer inserted into the center of loin registers 145°, 45–60 minutes. (The internal temperature of grill should be 400°; add more charcoal or adjust heat as needed.)
9. Transfer pork to a cutting board, tent loosely with foil, and let rest 20 minutes. Cut loin from ribs, and slice loin; cut between ribs. Serve with Peach Mustard.
10. Do ahead: Dry rub can be made 1 day ahead. Store airtight at room temperature.