Bring a pot of salted water to the boil. Add chopped potatoes and cook until tender, about 10–12 minutes.
Drain and mash with butter and milk until smooth. Season with salt and pepper.
While potatoes cook, heat oil in a frying pan over medium-high heat. Season steaks with salt and pepper, then sear for 3–4 minutes per side for medium-rare (adjust to preference). Rest for 5 minutes before slicing.
In a small pan, sauté sliced onions in a little oil until golden and soft.
Steam or boil the tenderstem broccoli until bright green and tender, about 3–4 minutes.
Warm or prepare gravy according to packet or recipe instructions.
Serve sliced steak with scoops of mashed potato topped with gravy, sautéed onions, and steamed broccoli.
