Make the marinade: In a large bowl or zip-top bag, whisk together 2 cups buttermilk, ½ cup pickle juice, 1 tablespoon salt, 1 teaspoon black pepper, 2 teaspoons garlic powder, and 2 teaspoons paprika.
Marinate the chicken: Add chicken thighs and legs to the marinade. Make sure everything is coated. Cover and refrigerate for at least 2 hours, but overnight is even better.
Make the flour dredge: In a shallow dish, whisk together 115g (1 cup) rice flour, 80g (½ cup) potato starch, 64g (½ cup) cornstarch, 2 teaspoons salt, 2 teaspoons garlic powder, 1 teaspoon onion powder, 1 teaspoon black pepper, and 2 teaspoons paprika.
Add brine to the flour: Take about ½ cup of the marinade and whisk it into the flour mixture.
This creates those craggy bits that fry up extra crispy.
Dredge the chicken: Remove chicken from the marinade and press each piece firmly into the flour mixture, making sure to coat all the nooks and crannies.
Let it rest: Place the coated chicken on a wire rack and let it sit for 10-15 minutes. This helps the coating set and stick better.
Heat the oil: In a large, heavy pot or Dutch oven, heat 3 inches of oil to 325°F.
Fry the chicken: Working in batches to avoid crowding, carefully add the chicken to the hot oil. Maintain oil temperature at 310-325°F.
Fry chicken legs for about 10-14 minutes and thighs for 12-16 minutes, flipping halfway through, until golden brown and internal temperature reaches 165°F. Use a thermometer to confirm the internal temperature of the chicken.
Drain and season: Transfer fried chicken to a wire rack set over a baking sheet. Immediately sprinkle with flaky sea salt while still hot.