1/2 cup kosher salt
1/2 cup sugar
1 teaspoon juniper berries
1/2 teaspoon whole black peppercorns
1 head of garlic, halved crosswise, plus 2 unpeeled cloves for basting
2 large sprigs thyme
1 2-inch-thick bone-in pork chop (2 ribs; about 1 1/4 lb.)
2 tablespoons grapeseed or vegetable oil
3 tablespoons unsalted butter
Flaky or coarse sea salt
Bring 2 cups water to a boil in a medium saucepan. Add kosher salt, sugar, juniper berries, peppercorns, halved head of garlic, and 1 thyme sprig; stir to dissolve salt and sugar. Transfer to a medium bowl and add 5 cups ice cubes. Stir until brine is cool. Add pork chop; cover and chill for at least 8 and up to 12 hours.
Preheat oven to 450°. Set a wire rack inside a rimmed baking sheet. Remove chop from brine; pat dry. Heat oil over medium-high heat in a large cast-iron or other oven-proof skillet. Cook chop until beginning to brown, 3-4 minutes. Turn and cook until second side is beginning to brown, about 2 minutes. Keep turning chop every 2 minutes until both sides are deep golden brown, 10-12 minutes total.
Transfer skillet to oven and roast chop, turning every 2 minutes to prevent it from browning too quickly, until an instant-read thermometer inserted horizontally into center of meat registers 135°, about 14 minutes. (Chop will continue to cook during basting and resting.)
Carefully drain fat from skillet and place over medium heat. Add butter, 2 unpeeled garlic cloves, and remaining thyme sprig; cook until butter is foamy. Carefully tip skillet and, using a large spoon, baste chop repeatedly with butter until butter is brown and smells nutty, 2-3 minutes.
Transfer pork chop to prepared rack and let rest, turning often to ensure juices are evenly distributed, for 15 minutes. Cut pork from bones, slice, and sprinkle with sea salt.