Place each steak on a flat working surface and using a meat mallet, pound until about 1/4-inch thick.
In a bowl, combine cube steaks and the buttermilk. Marinate in the refrigerator for about 2 to 4 hours. Drain well, reserving 1/4 cup of the buttermilk. Pat the cube steaks dry and season with salt and pepper to taste.
In a shallow plate, combine flour, corn starch, baking powder, salt, garlic powder, onion powder, paprika, pepper, and cayenne pepper.
In a shallow baking dish, combine egg and the reserved 1/4 cup buttermilk and whisk until blended.
Working with one steak at a time, dredge in flour mixture, dip into egg mixture and then in the flour mixture again until fully coated. Arrange breaded steaks in a single layer on a wire rack and let stand for about 3 to 5 minutes. Reserve 2 tablespoons of the flour mixture.
In a cast iron skillet or thick-bottomed pan over medium heat, heat about 1/2- inch deep of oil to 350 F (until the oil is shimmering but not smoking).
Add steaks one at a time into the hot oil and fry for about 2 to 3 minutes on each side or until or until golden brown and cooked through. Remove from pan and drain excess oil on a wire rack. Keep warm and proceed with making the cream gravy.