Choose a thick filet mignon, about 1.5 to 2 inches thick
Pat the steak completely dry with paper towels
Season generously with kosher salt and black pepper
Let the steak sit at room temperature for 20 to 30 minutes
Preheat the oven to 400°F
Heat a cast-iron skillet over high heat until very hot
Add a small amount of high-smoke-point oil to the skillet
Sear the steak for 2 to 3 minutes without moving it
Flip the steak and sear the other side for 2 to 3 minutes
Sear the edges briefly if needed
Add butter, garlic, and fresh herbs to the skillet
Spoon the melted butter over the steak for 30 to 60 seconds
Transfer the skillet to the oven
Roast until the internal temperature reaches 125°F for rare, 130°F for medium-rare, or 140°F for medium
Remove the steak from the skillet
Rest the steak on a plate or cutting board for 5 to 10 minutes
Slice and serve immediately