Let the beef tenderloin steaks come to room temperature before cooking. Take them out of the fridge about an hour before starting this dish.
Preheat the oven to 425-F.
Add 1 tbsp oil and 1 tbsp butter to the oven-safe skillet and sautee the garlic and mushrooms for two minutes. Remove mushrooms and garlic.
Season the steaks well with salt and pepper. Add the remaining oil and butter to the skillet and heat until very hot but not smoking.
Add the steaks and sear about 2 minutes per side. You're looking for a good, dark sear, but don't burn them!
Add the mushrooms to the skillet and pop the whole skillet into the heated oven. Cook for about 4 minutes at 425-F for medium-rare. Use a digital meat thermometer to get an accurate internal temperature.
Remove the steaks and let rest for about five minutes before serving.
Cooking times are approximate, but use this guide to help you cook your steaks:rare, 120F internal temperature, 4 minutes in the ovenmedium rare, 125F internal temperature, 5-6 minute in the ovenmedium, 130F internal temperature, 6-7 minutes in the oven