METHOD
1. Trim and clean the beef tenderloin. Cut four châteaubriand (beef tenderloin) steaks, each 4cm thick (about 170g per person). Dice the trimmings into small cubes and keep them refrigerated.
2. Pre-heat the deep fryer to 160°C. Meanwhile, peel, wash, and cut the potatoes into fine julienne. Rinse thoroughly under cold water to remove the starch, drain, and dry. Fry in deep fryer until golden and crispy. Drain, season with fine salt, and keep warm.
3. Clarify 200g of the unsalted butter: melt it gently to separate the milk solids (white liquid) from the clarified butter. Keep only the clarified part.
4. Peel, wash, and finely chop the shallots, then remove tarragon leaves from the stems; finely chop the leaves, and reserve stems.
5. In a saucepan, reduce white vinegar with a teaspoon of cracked pepper, the tarragon stems, and half of the chopped shallots.
6. Allow the vinegar to fully evaporate over low heat, then cool.
7. Add 3 egg yolks and 50ml water to the cooled reduction. Over low heat, whisk vigorously in a figure eight motion. When the yolks thicken and the bottom of the pan becomes visible with each stroke, the sabayon (sauce) is cooked. Season with salt and gradually whisk in the clarified butter. Strain the sauce, add the chopped tarragon, and keep warm in a bain marie.
8. Pre-heat oven to 180°C. Season the châteaubriand steaks with fine salt and a touch of cracked pepper. In a hot sauté pan, brown the steaks on all sides in nut brown butter. Transfer the steaks to a baking dish, scatter the trimmings around them, and roast for 2 x 5 minutes, turning and basting with the cooking butter halfway through. Transfer to a rack and let rest in a warm place.
9. Add the remaining chopped shallots to the sauté pan. Deglaze with the white and red wines, reduce, then add the chicken stock. Simmer gently to obtain a concentrated jus. Strain and finish with a small knob of butter. Check seasoning and plate as pictured.