Combine the olive oil, salt, pepper, rosemary, chili, and celery seed in a shallow dish and smear the filet mignon with the spiced ointment. Marinate for 10 minutes at room temperature. On medium-high heat, pan-sear the steak for 4 minutes on its first side, then 3 minutes on its second side; you should hear a hot sizzle all the way. Transfer to the bottom rack of an oven for 3-5 minutes depending on the thickness of your steak and desired doneness. This last step is the most important: let your meat rest for at least 5 minutes so the juices can redistribute.