Preheat your grill to HIGH (e.g., 450°F).
Brush each filet mignon with olive oil, then season generously with salt and pepper.
Place the filets on the hot grill and cook for 3-4 minutes (rare), 4-5 minutes (medium-rare), 5-6 minutes (medium) on one side, without moving them to get a good sear.
Flip the steaks and grill for the same amount of time.
While the steaks are grilling, mix together the softened butter, chopped rosemary, tarragon, and minced garlic in a small bowl.
Once the steaks are done, transfer them to a plate and immediately top each with a dollop of the prepared herb butter.
Let the steaks rest for 5 minutes before serving to allow the juices to redistribute.