Preheat a fryer to 360 degrees F.
Combine balsamic vinegar, olive oil, salt, pepper, and 1 tablespoon parsley. Add steak and marinate for at least 2 hours.
Pan sear or grill marinated sirloin over high heat for 45 seconds on both sides and cut into 1/4-inch strips.
Fry skin-on fries until very crisp. Drain on a paper towel-lined plate. Toss fries and sirloin together with garlic butter, Parmesan, and remaining chopped parsley.
Using the back of a fork, blend all ingredients together until evenly distributed.