Roast beef is always cooked as a whole piece—preferably seared on the outside and still nice and rare on the inside. So start by searing the roast beef in butter, then let it cook through slowly over low heat or in the oven (max 160°C / 320°F) until it reaches an internal temperature of around 50°C / 122°F. A good meat thermometer is really useful for roasts like this—almost essential! If roast beef cooks too long, it loses color, flavor, and moisture, which makes the meat tougher. And that’s exactly what you don’t want!