Peel the potatoes, cut into chips, wash until water runs clear, and pat dry.
Heat vegetable oil in a deep pan to between 140°C and 160°C.
Fry chips for 8 minutes until cooked but not colored, then drain and cool.
Increase oil temperature to 180°C and fry chips again for 2 minutes until golden.
Slit the steak fat, drizzle with oil, and sear the fatty edge in a hot griddle pan.
Season steak and grill for 2 to 4 minutes per side depending on preferred doneness.
Rest the meat on a warm plate for several minutes before serving.
Serve the finished steak and chips with a side of Dijon mustard.