Preheat the oven to 400°F (200°C).

In a small skillet over medium heat, toast the mustard seeds until they begin to pop, about 2-3 minutes. Remove from heat and let cool.

In a small bowl, combine the toasted mustard seeds and chopped rosemary. Set aside.

Season the filet mignon steaks generously with salt and black pepper on both sides.

In a large oven-safe skillet, heat the olive oil over high heat. Once hot, add the filet mignon steaks and sear for about 3-4 minutes on each side until a nice crust forms.

Remove the skillet from the heat. Press the mustard seed and rosemary mixture onto the top of each steak.

Transfer the skillet to the preheated oven and roast the steaks for about 5-7 minutes for medium-rare, or longer for your preferred doneness.

While the steaks are roasting, prepare the roasted garlic butter. In a bowl, mash the roasted garlic cloves with a fork. Mix in the softened butter and lemon juice until well combined. Season with salt to taste.

Once the steaks are cooked to your liking, remove them from the oven and let them rest for 5 minutes.

Serve the filet mignon topped with a dollop of roasted garlic butter and garnish with fresh rosemary sprigs. Enjoy!