Chateaubriand with wine and mushroom sauce and mashed potatoes

Ingredients:

Chateaubriand and wine-mushroom sauce

• 0.7 kg chateaubriand steak (center cut of beef tenderloin), trim fat and remove membrane, tie meat with kitchen string at 1 cm intervals.
• 3 tablespoons extra-virgin olive oil
• 4 tablespoons unsalted butter
• 1.5 cups quartered mushrooms, such as button mushrooms, shiitake mushrooms, or chanterelle mushrooms
• 4 cloves garlic, peeled and crushed
• 4 sprigs fresh thyme + extra leaves for serving
• 2 tbsp chopped shallots
• 0.5 cups dry red wine
• 2 cups beef broth
• 1/4 cup heavy cream
• Marrow bones, see recipe below

Mashed potatoes

• 0.9 kg potatoes, peeled and cut into 5-7 cm pieces.
• 2 cups chilled heavy cream
• 3 cloves of garlic
• 110 g unsalted butter, cut into pieces
• Extra-virgin olive oil
• Coarse sea salt

Preparation:

1. Boil the potatoes:
   
   In a medium saucepan, combine the potatoes with the cream, garlic, butter, and a pinch of coarse salt. Bring to a boil over medium-high heat, then reduce the heat to medium-low and simmer until the potatoes are easily pierced with a fork, about 25 minutes.
2. Make a chateaubriand:
   
   Preheat oven to 350°F (175°C). Let the beef rest at room temperature for 15 minutes, then season with salt and black pepper. In a large, oven-safe skillet, heat the olive oil over high heat until shimmering, about 2 minutes. Add the roast to the skillet and sear on all sides until browned, about 8 minutes total. Reduce heat to low and add 2 tablespoons butter, the mushrooms, garlic, and thyme. Transfer the skillet to the oven and roast the beef until a meat thermometer inserted into the thickest part of the tenderloin registers 125–135°F (51–54°C), 6–8 minutes for medium-rare. Remove the skillet from the oven, transfer the roast to a cutting board, cover loosely with foil, and let it rest for 10 minutes. Prepare the marrow bones according to the recipe - Baked marrow bones.
3. Make red wine sauce:
   
   Transfer the mushrooms to a bowl and drain most of the fat from the pan, reserving only 1 tablespoon (discard the garlic and thyme). Return the pan to medium heat, add the shallots and red wine, and cook, stirring and scraping up any browned bits from the bottom of the pan, until almost dry, about 2 minutes. Add the broth and cream, bring to a simmer, and cook until the sauce thickens, 3-5 minutes. Return the mushrooms to the pan and season with salt and pepper, if needed.
4. Prepare mashed potatoes:
   
   Place a colander over a large bowl. Place the hot potatoes in the colander. Shake the potatoes to remove excess water. Press the potatoes through a potato masher (or mash them with a fork if you prefer chunky potatoes) into a medium bowl, scraping the edges of the masher occasionally with a spoon. Pour the reserved, still-hot cream over the potatoes in small portions, stirring until the desired consistency is achieved. Drizzle the mashed potatoes with olive oil, sprinkle with sea salt, and serve immediately or keep in a warm oven at 100°C.
5. To serve, trim the roast and cut it crosswise into two equal pieces. Season with salt and black pepper. Divide the mashed potatoes between two warm plates. Place a piece of beef on each plate and top with the wine-mushroom sauce. Arrange the roasted bones. Garnish with fresh thyme leaves and serve.