In a food processor, combine garlic and rosemary and pulse until finely chopped. (Or chop finely by hand.)
Rub pork loin with garlic mixture, salt and pepper. Set in a large bowl and cover with balsamic, Worcestershire sauce and oil. Let pork marinate for 1-2 hours in the refrigerator. Pull 30 minutes before cooking and let it come to room temperature.
Preheat oven to 400° F. Put pork in a greased baking dish or cast-iron skillet and bake until it reaches an internal temperature of 140° F, turning once halfway in between. The time it takes will vary, depending on size, but ours usually take around 30 minutes. Start checking around 20 minutes.
Pull pork from oven and cover. Let rest 10 to 15 minutes before carving. Enjoy!
This recipe is for a small tenderloin. To make a larger pork loin, Turn oven temperature down to 375° F after 20 minutes and continue to cook until the center reaches 140° F. It will take a bit longer, about an hour.