Let your steaks sit out of the fridge for 30 minutes before you start. This helps them cook more evenly.
Pat the filets dry with paper towels, then season all sides with a generous amount of kosher salt and cracked black pepper.
Heat a skillet over high for a minute or two until it’s very hot, then pour in the olive oil.
When the oil starts shimmering, lay your steaks in and sear each side for about 2 minutes. You want a deep brown crust.
Turn the heat down to medium, toss in the butter, rosemary, and garlic, and tilt the pan so you can spoon the melted butter over the steaks for a minute or two.
Pop the whole skillet in a preheated oven at 400°F and roast for 5-7 minutes if you’re after medium-rare.
Let the steaks rest on a plate, loosely covered with foil, for at least 5 minutes before serving.