In a small bowl, combine the softened butter, mashed black garlic, lemon zest, and lemon juice. Mix until well combined. Set aside.

Heat 1 tablespoon of olive oil in a skillet over medium-high heat. Add the sliced leeks and season with salt and pepper. Cook until the leeks are charred and tender, about 5-7 minutes. Stir in the fresh thyme and cook for an additional minute. Remove from heat and set aside.

Preheat a grill or skillet over high heat. Pat the filet mignon steaks dry with paper towels and rub both sides with the remaining olive oil. Season generously with salt and pepper.

Place the steaks on the hot grill or skillet. Cook for about 4-5 minutes on each side for medium-rare, or until desired doneness is reached. Remove the steaks from the heat and let them rest for 5 minutes.

On each plate, place the charred leeks. Top with the filet mignon steaks. Slice the black garlic compound butter and place a slice on top of each steak, allowing it to melt over the warm meat.

Garnish with additional fresh thyme if desired and enjoy your delicious charred leek and fresh thyme-crusted filet mignon!