Step 1: Remove the beef from the refrigerator 45 minutes before cooking and season generously with salt and pepper on all sides.
Step 2: Preheat your oven to 400°F (200°C).
Step 3: In a large oven-proof skillet, heat olive oil and 1 tablespoon of butter over medium-high heat until shimmering.
Step 4: Sear the beef tenderloin for 3-4 minutes per side until a deep golden crust forms, then transfer the skillet to the oven.
Step 5: Roast until the internal temperature reaches 130°F (54°C) for medium-rare, approximately 15-20 minutes.
Step 6: Remove the beef from the skillet and place it on a cutting board to rest for at least 10 minutes.
Step 7: In the same skillet over medium heat, add the remaining butter and the sliced mushrooms. Sauté until browned.
Step 8: Stir in the garlic and herbs, cooking for 1 minute until fragrant.
Step 9: Pour in the wine to deglaze, scraping the bottom of the pan, then add the beef stock and simmer until the sauce reduces by half.
Step 10: Slice the beef and spoon the hot mushroom sauce over the top before serving.