Whisk together buttermilk, eggs, and hot sauce in a shallow dish. Place pieces of cube steak into the buttermilk to marinate for one hour on the counter, up to overnight in the refrigerator. Remove from the refrigerator 30 minutes before you’re ready to fry your steaks. In the meantime you can make your biscuits.
Whisk together flour with salt, paprika, black pepper, onion powder, garlic powder, baking powder, and optional cayenne pepper in a shallow dish.
Place ½ inch of oil in a 12 inch cast iron skillet, or other large heavy bottom pan, and heat to 325°F over high heat. If you don't have a thermometer, the oil should sizzle if you drop a bit of flour on its surface.
Remove steak pieces from the buttermilk, letting excess drip off.
Working with one or two pieces at a time, dredge steak pieces in the flour, shaking off the excess, patting flour into the steaks with your hands.
Carefully place your steaks into oil. Cook on the first side until golden brown and crisp, about 3 to 4 minutes. Flip over and cook on the other side.
Transfer to a wire rack set into a paper towel lined large sheet pan and season with a pinch of salt. Repeat with remaining steaks. Keep steaks and biscuits warm in a 200° oven while you make the gravy.