Let tenderloin sit at room temperature for 1 hour before cooking.

Preheat oven to 450˚F.

In a small bowl mix together minced garlic and chopped rosemary; rub all around the tenderloin.

Place tenderloin over pieces of precut kitchen twine spaced one-inch apart and tie them closed. You can also ask the butcher to tie the tenderloin for you.

Heat vegetable oil in a 12-inch cast iron skillet over medium-high heat.

When oil is hot, add tenderloin and sear for about 3 to 4 minutes per side, or until browned all around.

Transfer skillet to the oven and continue to cook for 25 to 30 minutes, or until internal temperature reaches 130˚F. Cooking time can vary depending on your oven and the thickness of your tenderloin; always check for desired doneness using a meat thermometer.

Remove skillet from oven and transfer meat to a cutting board.

Tent a piece of foil over the tenderloin and let rest for 10 to 15 minutes before cutting.

Cut into 1/2-inch slices and serve.