Ingredients :

• Whole beef tenderloin (900 g) — This is the piece that decides everything. A whole tenderloin, not pre-cut tournedos. Get it from a butcher, not plastic-wrapped in a supermarket. Ask them to trim it for even cooking — the thin ends cook faster and can dry out if you’re not careful.
• Softened unsalted butter (60 g) — It must be at room temperature, soft as modeling clay — not melted, and not pulled from the fridge five minutes before. Churned or premium butter makes a real difference here: more fat, more flavor, and a better crust.
• Fresh rosemary and thyme — Fresh, not dried. Dried herbs burn before providing fragrance at high temperatures and give a dusty taste. Chop the rosemary finely, and strip the thyme by sliding your fingers down the stem. If you only have one, double the dose of the other; it works fine.
• Salt and pepper — Fine salt in the butter so it penetrates the meat while cooking. Save the sea salt flakes for the slices at the moment of serving — they crunch slightly and wake everything up. Freshly ground black pepper only, not pre-powdered pepper that has lost half its aroma.