In a mixing bowl, combine the buttermilk, chicken thighs, salt, and pepper. Cover and refrigerate for at least 30 minutes.
In another bowl, whisk together the flour, paprika, garlic powder, onion powder, salt, and pepper.
Heat oil in a frying pan or deep fryer to 350°F (175°C).
Remove the chicken from the buttermilk marinade and allow excess to drip off. Dredge each piece in the flour mixture, ensuring they are fully coated.
Carefully place the coated chicken into the hot oil. Fry for about 5-7 minutes until golden brown and cooked through. Drain on paper towels and set aside.
Preheat the oven to 450°F (230°C) while the chicken is frying.
In a bowl, combine flour, baking powder, and salt. Cut in the cold butter until the mixture resembles coarse crumbs. Stir in the milk until just combined.
Turn the dough onto a floured surface. Gently knead a few times, then roll it out to about 1-inch thickness. Cut out biscuits using a biscuit cutter or glass.
Place the biscuits on a baking sheet and bake for 12-15 minutes until they are golden brown.
To assemble the sandwiches, split the biscuits in half, place a piece of fried chicken on the bottom half, and add a slice of cheddar cheese and desired toppings before capping with the biscuit top.