Preheat your oven to 400°F (200°C).

In a small bowl, combine the chopped roasted chestnuts, crushed coriander seeds, salt, and pepper.

Rub the beef tenderloin with olive oil and season with additional salt and pepper.

Press the chestnut and coriander mixture evenly over the entire surface of the beef tenderloin, ensuring it adheres well.

Heat a large cast-iron skillet or oven-safe pan over medium-high heat. Once hot, add the beef tenderloin and sear on all sides until golden brown, about 3-4 minutes per side.

Transfer the skillet to the preheated oven and roast the beef for about 25-30 minutes, or until it reaches your desired level of doneness (135°F for medium-rare).

While the beef is roasting, prepare the browned sage and thyme butter. In a small saucepan over medium heat, melt the unsalted butter.

Add the minced garlic and cook for about 1-2 minutes until fragrant.

Stir in the sage and thyme leaves and continue to cook until the butter turns a golden brown color, about 2-3 minutes. Remove from heat and set aside.

Once the beef tenderloin is done, remove it from the oven and let it rest for 10 minutes before slicing.

Serve the sliced beef drizzled with the browned sage and thyme butter.