Preheat oven to 425 def F

Coat filets with oil and season. Preheat cast iron in oven and for a couple minutes over a burner on high heat.

Sear fillets for about 2 min per side

Top each with some butter and put in preheated oven at 425 deg for 9-11 min, check meat with thermometer to confirm desired doneness

Transfer steaks to a platter and cover tightly with aluminum foil. Let them sit for 5-10 min