Country-Fried Steak with Mushroom Gravy

You might know a rustic-style steak as fried with chicken, depending on where you live. We recommend diced steak, but you can buy a regular tenderloin steak and chop it with a rolling pin. For making mashed potatoes, it is better to use a frozen variety.
Combine 3 tablespoons of milk and egg whites in a shallow bowl, stirring with a whisk. Combine 1/3 cup flour and the next 4 ingredients (1/3 cup flour and pepper) in a shallow bowl. Cook 1 steak at a time, dipping in egg mixture; roll in flour mixture. Repeat with the remaining steaks, egg mixture, and flour mixture.Heat the oil in a large nonstick skillet over medium-high heat. Add the steaks; cook for 3 minutes on each side or until lightly browned. Remove the steaks from the pan; keep warm.While the steaks are cooking, prepare the mashed potatoes according to the instructions on the package, using 1/3 cup of milk. Keep warm.Add the mushrooms to the pan; saute for 3 minutes. Combine 2 1/2 tablespoons flour, 1/4 teaspoon salt, and stock, stirring with a whisk. Add the stock mixture to the pan. Bring to a boil; cook for 1 minute, stirring constantly. Spoon over the steaks. Serve with mashed potatoes.