Remove the rump steaks from the refrigerator at least one hour before cooking to allow them to come to room temperature.
Combine all Café de Paris butter ingredients until smooth. Spoon onto baking paper, roll into a log and refrigerate until firm.
Preheat the oven to 110°C.
Season the steaks generously with sea salt and cracked black pepper.
Place the steaks onto a wire rack over a baking tray and cook in the oven for approximately 25–30 minutes, or until the internal temperature reaches around 48–50°C.
Heat a cast iron pan or barbecue until smoking hot.
Add the olive oil and sear the steaks for approximately 60–90 seconds on each side.
Add the butter, garlic and rosemary to the pan and baste the steaks continuously for another minute.
Remove from the heat and rest for 8–10 minutes.
Slice thickly across the grain and top with generous rounds of Café de Paris butter so it slowly melts over the steak.
Serve immediately.