Whisk together the 2 cups buttermilk and 1 large egg in a large bowl. Add all 8 chicken pieces, cover, and refrigerate for at least 4 hours or overnight.

In a wide shallow bowl, whisk together the 2 cups flour, 3 tbsp cornstarch, 1 tsp salt, 1 tsp black pepper, 1 tsp garlic powder, 1 tsp onion powder, 1 tsp paprika, 1 tsp dried thyme, 1 tsp dried basil, 1/2 tsp dried oregano, 1/2 tsp celery salt, 1/2 tsp white pepper, and 1/4 tsp cayenne.

Remove each piece from the buttermilk, dip in the flour, back into the buttermilk, then press firmly into the flour a second time. Rest coated pieces on a wire rack for 30 minutes.

Heat the 4 cups oil in a Dutch oven to 325°F (163°C). Fry the thighs and drumsticks in batches for 15 to 17 minutes, turning once, until the crust is deep amber and internal temp reads 165°F (74°C). Transfer to a wire rack.

Return the oil to 325°F (163°C) and fry the breast pieces for 13 to 15 minutes and wings for 10 to 12 minutes, turning once, until each reaches 165°F (74°C) internally.

Arrange all pieces on a serving platter, sprinkle with flaky sea salt and a pinch of paprika, and serve immediately.