Bacon fat complements nearly any food you pair it with, from ice cream and chocolate to burgers and cheesy fries. Flavoring is only one item on bacon's long list of uses -- it's also used for barding. Barding is a technique that helps lean meats stay moist, and the reason you often find poultry and lean beef studded with fatty bacon. Filet mignon, the wonderfully tender but notoriously lean cut of tenderloin, is the most commonly barded steak. Bacon, when combined with quick cooking, helps your fillets turn out tender and moist every time.
Take the fillets and bacon out of the fridge about 30 minutes before you want to cook them. You want the bacon ready to render as soon as it hits the pan.
Pat the fillets dry with paper towels and season them to taste on the top, bottom and sides with kosher salt and freshly ground black pepper.
Wrap one piece of thick-cut, fatty bacon around each fillet and secure it with a toothpick. It's OK if the bacon overlaps itself.
Heat butter and oil in a heavy-bottomed saute pan on the stove over medium-heat. Add a fresh-herb sprig -- rosemary is a classic for filet mignon -- to the fat in the pan as it heats. Fat extracts the essential oils in the herbs, which mingle with the pan juices and rendered bacon fat to flavor the fillet. The herb sprig also lets you know when the oil is hot enough to cook the fillet.
Place the fillets in the pan as soon as the fat starts to bubble around the herb sprig. Space the fillets at least 1 inch apart.
Sear the fillets on both sides until a pronounced golden-brown crust forms, about three minutes total, and lower the heat to medium.
Tilt the pan back towards you slightly and scoop the fat in the pan up and baste the fillets with it frequently. Spoon-basting bathes the fillets in bacon fat and herb oil, ensuring not any part of them go untouched during cooking.
Turn the fillets over frequently with tongs during cooking. Frequent turning helps ensure both sides of the fillets cook at the same speed.
Cook the fillets for a total of about 10 to 12 minutes, including the initial searing, to reach the recommended internal temperature of 145 degrees Fahrenheit. Take the fillets out of the pan.
Raise the heat on the stove to medium high. Remove the bacon and hold a fillet with the tongs.
Sear the fillets on the sides -- the portion that was covered with bacon -- one at a time in the saute pan until golden brown, about one minute total.
Take the steaks out of the pan and let them rest for about 10 minutes. Check the internal temperature by inserting a meat thermometer horizontally in the side of a fillet.