In a small bowl, combine the softened bone marrow, minced black garlic, chopped chives, and white truffle oil. Mix well until fully combined. Season with a pinch of salt and pepper to taste. Set aside.

In a skillet over medium heat, add the diced pancetta. Cook until crispy, about 5-7 minutes. Remove from the skillet and transfer to a paper towel-lined plate to drain excess fat.

Preheat your oven to 400°F (200°C). Pat the filet mignon steaks dry with paper towels. Season generously with coarse sea salt and cracked black pepper on both sides.

In the same skillet used for the pancetta, add a drizzle of olive oil and heat over medium-high heat. Once hot, add the seasoned filet mignon steaks. Sear each side for about 3-4 minutes until a nice brown crust forms.

Remove the skillet from the heat. Press the crispy pancetta onto the top of each filet, ensuring it's well coated.

Transfer the skillet to the preheated oven and bake for 5-7 minutes for medium-rare, or until desired doneness is reached.

Remove the skillet from the oven. Let the steaks rest for a few minutes before serving. Top each filet with a generous dollop of the black garlic and chive bone marrow butter. Serve immediately.