Butternut squash purée
Bring a large saucepan of water to a boil, add a pinch of coarse salt, and cook the squash until it is soft, about 15 minutes.
Remove the squash using a spoon, reserving the cooking water. Blend the squash with butter until smooth; season.
Butternut squash brunoise
Bring the reserved cooking water to a boil. Cook the butternut squash brunoise until soft, 3 - 5 minutes. Drain and keep warm.
Whisk the sherry vinegar, salt and pepper in a bowl until they have combined.
Once combined, whisk in hazelnut oil and chopped hazelnuts.
Cut a criss-cross at the base of each Brussel’s sprout.
Bring a large saucepan of water to a boil and add a pinch of coarse salt. Gently lower the sprouts into the boiling water and cook until vivid green, about 5 to 10 minutes.
Cut each sprout in half. Heat butter in a frying pan over medium high heat and fry Brussel’s sprouts until golden, about 2 to 5 minutes. Keep warm.
Sautéed beef tenderloin
Remove the beef tenderloin from the refrigerator 5 to 10 minutes prior to preparation time for even cooking. Season with the salt and pepper.
Heat the oil in a frying pan. When the oil is hot, cook to your preference, about 10 minutes for medium, turning once and sealing the edges. Spoon the oil over the beef to keep it moist.
Once cooked, remove from the heat and rest on a rack for 10 minutes.
Red wine sauce
Degrease the frying pan by blotting with absorbent kitchen paper. Add red wine, scrape the bottom of the pan with a wooden spatula to dislodge the pan drippings and simmer over medium heat. Reduce to syrup-like consistency, about 5 minutes. Add the veal stock and thyme. Reduce until sauce coats the back of a spoon, about 5 minutes.
Strain through a chinois, whisk in butter, and season.
Reheat the butternut squash purée. Place a spoonful of purée in the center of the plate, smooth into a circle using the back of a spoon. Place the beef tenderloin on top.
Lightly dress the Brussel’s sprouts with the hazelnut vinaigrette and arrange on the plate.
Spoon the red wine sauce onto the beef. Garnish with butternut squash brunoise. Decorate with some Brussel’s sprout leaves and chervil.