Peel the potatoes and cut into 1cm square chips roughly 7cm long.
Rinse chips in cold water and dry thoroughly with kitchen towels.
Heat vegetable oil in a deep pan to 140°C–160°C.
Fry chips for eight minutes until just cooked through and drain on paper.
Increase oil temperature to 160°C–180°C.
Heat a ridged grill pan until hot and brush steaks with oil.
Season steaks with salt and pepper and place on the hot grill.
Turn steaks 90 degrees after a few minutes to create diamond grill marks.
Flip steaks and cook until desired doneness, then remove to rest.
Fry the chips a second time for 2–3 minutes until golden and crisp.
Drain chips and serve with steaks, grilled tomatoes, and mustard.