Take the filet mignon steaks out of the refrigerator and let them rest at room temperature for about 30 minutes. Preheat your oven to 400°F (200°C).

Pat the steaks dry with paper towels. Season generously with salt and pepper on both sides. Spread a thin layer of the mashed fermented black garlic on top of each steak.

In a shallow dish, spread the crushed roasted hazelnuts. Press the black garlic-coated side of each steak into the hazelnuts.

In a large oven-safe skillet, heat the olive oil over medium-high heat. Once hot, add the steaks crust-side down. Sear for about 3-4 minutes.

Carefully flip the steaks over and sear the other side for another 2 minutes. Transfer the skillet to the preheated oven and roast the steaks for about 6-10 minutes.

While the steaks are in the oven, prepare the sauce. In a small saucepan, combine cognac and beef stock over medium heat. Bring to a simmer and let it reduce by half, about 10-15 minutes.

Once reduced, remove from heat and stir in black truffle oil. Season with salt and pepper to taste.

Once the steaks are done, remove them from the oven and let them rest for about 5 minutes. Slice the filet mignon and plate it.

Drizzle the cognac-black truffle reduction over the top and garnish with fresh herbs if desired. Serve immediately and enjoy!