Step 1

Lay racks of pork flat on work surface, meaty side down (the inside of the ribs should be facing up). Use a knife to make 3 vertical 3"-long slits (about 1" deep) into the loins of each rack, 1 slit between every 2 ribs. Place each rack of pork into a 1-gal. resealable plastic bag and chill.

Step 2

Heat brown sugar, salt, and 4 cups water in a large saucepan over medium, stirring until sugar and salt are dissolved, about 5 minutes. Remove from heat and add vinegar and 4 cups ice water. Chill brine until cold, about 1 hour.

Step 3

Divide brine between bags with pork and seal, squeezing out excess air; chill pork 8–24 hours.

Step 4

Remove pork from bags and pat dry. Place on a large rimmed baking sheet; let sit 2 hours to bring to room temperature.

Step 5

Preheat oven to 300°. Mix garlic, chopped thyme, mustard seeds, pepper, ¼ cup mustard, and 2 Tbsp. oil in a small bowl. Smear all over pork, working into slits; tuck thyme sprigs into slits. Upend both racks so they’re parallel to one another with bones facing up and slits facing out. Curve racks toward each other so they meet at both ends to form a crown (call a friend to help with this part). Holding pork in place, encircle racks with string and tie securely in 2 places: around rib bones and around thickest part of loin. If desired, wrap tops of bones individually with foil to keep them from burning.

Step 6

Heat remaining 2 Tbsp. oil in a large skillet over medium. Cook bacon, stirring often, until fat is rendered and edges are crisp, about 5 minutes. Transfer bacon to a roasting pan with a slotted spoon.

Step 7

Working in 2–3 batches, add apples, cut side down, and shallots to same skillet and cook over medium-high heat (undisturbed) until golden brown, about 5 minutes. Transfer apples to roasting pan; turn shallots and cook until golden brown on the other side, about 3 minutes. Transfer to roasting pan.

Step 8

Remove skillet from heat and carefully add cider, stirring and scraping up any browned bits. Pour liquid into roasting pan and place pork in the center, pushing apples and shallots to the edges; reserve skillet. Roast pork until an instant-read thermometer inserted into the center of loin registers 135°, 1¾–2¼ hours.

Step 9

Remove roast from oven and transfer apples and shallots to a platter; tent with foil. Increase oven temperature to 500°. Transfer pork to a cutting board and pour pan juices into reserved skillet. Return pork to roasting pan; roast until browned and crisp all over, 5–10 minutes. Transfer roast back to cutting board and let rest 30–45 minutes before cutting into chops.

Step 10

Just before serving, whisk remaining 2 Tbsp. mustard into pan juices in skillet and bring to a simmer over medium heat. Cook, whisking often, until sauce is reduced to about 1 cup, 7–10 minutes.

Step 11

Transfer pork chops to platter with apples and shallots; spoon sauce over.