Preheat your oven to 400°F (200°C).

In a dry skillet over medium heat, add the sesame seeds. Toast them for about 3-4 minutes, stirring frequently, until they are golden brown and fragrant. Remove from heat and let cool.

In a small bowl, mix the softened butter with wasabi paste, chopped chives, and soy sauce until well combined. Set aside.

Season the filet mignon steaks generously with salt and pepper.

In the same skillet used for toasting the sesame seeds, heat the olive oil over medium-high heat. Once hot, add the filet mignon steaks and sear for 2-3 minutes on each side, or until a golden-brown crust forms.

Remove the steaks from the skillet and place them on a baking sheet. Evenly coat the top of each steak with the minced lemongrass and then sprinkle the toasted sesame seeds over the lemongrass, pressing gently to adhere.

Transfer the baking sheet to the preheated oven and roast the steaks for about 5-7 minutes for medium-rare, or adjust the time for your desired doneness.

Once cooked to your preference, remove the filet mignon from the oven and let rest for 5 minutes before serving.

Serve the steaks with a dollop of the wasabi-chive butter on top, allowing it to melt over the warm meat.