Place 1 cup of the milk in a medium bowl or pie plate. Add cubesteaks to milk, then soak 15 minutes.
Whisk together flour, seasoning salt, garlic powder and ¼ teaspoon black pepper in a shallow bowl or pie plate. Remove 1 of the steaks from the milk, allowing excess milk to drip off. Dredge steak in flour mixture, turning to coat evenly on all sides. Transfer to a parchment paper-lined baking sheet. Continue with remaining steaks. Reserve flour mixture to make gravy.
Heat oil in a large (12-inch) cast iron skillet over medium. When oil is hot (about 350ºF), add 2 steaks to skillet and fry until golden brown and cooked through, about 6 to 8 minutes, turning steaks a few times to ensure even browning. Remove steaks to a paper towel-lined plate, then continue frying remaining 2 steaks.
Discard all but 2 tablespoons of the frying oil. Let oil come back up to temperature, then add 2 tablespoons of the reserved flour mixture to hot oil. Whisk flour mixture into oil and cook until raw flour smell dissipates and begins to turn golden brown and smell nutty, about 90 seconds. Slowly whisk in remaining 2 cups milk until gravy is creamy and thick. Whisk in more milk if gravy becomes too thick before serving. Serve gravy with cubesteaks and garnish with black pepper.
