In a zip-top bag, place the olive oil, balsamic vinegar, rosemary, and pepper. Squeeze the bag to mix.
Place the pork tenderloin in the bag and place it in the refrigerator to marinate, from 30 minutes to overnight. Turn the bag occasionally.
Preheat oven to 375 degrees.
Heat an oven-proof skillet on the stove over medium-high heat. Remove the tenderloin from the bag and place it in the heated pan; discard the remaining marinade.
Sprinkle salt over the pork tenderloin and sear the pork for two minutes per side until nicely browned. Place the skillet into the oven and roast the pork for 15-20 minutes or until pork reaches an internal temperature of 150 degrees.
Remove from the oven and allow to rest for five minutes.. Slice into 1/2-inch rounds and serve.