Place the chicken thighs in a bowl and pour 1 cup of buttermilk over them. Turn to coat, cover, and refrigerate for at least 1 hour or up to overnight.

In a large bowl, mix 2 cups of flour with 1 teaspoon salt, black pepper, paprika, and garlic powder. Remove the chicken from the buttermilk and dredge each piece in the seasoned flour, pressing to coat well.

Heat 1 inch of vegetable oil in a large cast-iron skillet over medium heat until it reaches 350°F. Fry the chicken in batches for 6 to 8 minutes per side until golden and cooked through. Drain on a wire rack.

Heat the oven to 425°F. In another bowl, whisk together the remaining 1 cup of flour, 1 teaspoon salt, baking powder, and baking soda. Cut in the cold butter until the mixture looks like coarse crumbs.

Stir in the remaining 1 cup of buttermilk just until a soft dough forms. Turn the dough onto a lightly floured surface, pat it into a 1-inch thick rectangle, and cut into 4 squares.

Place the biscuits on a baking sheet and bake for 12 to 15 minutes until golden on top. Serve warm alongside the fried chicken.