Mix balsamic vinegar, garlic powder, rosemary, salt, and pepper together in a small bowl.
Rub marinade over pork tenderloin and let sit 20 minutes at room temperature. Flip pork at 10 minutes to get marinade on both sides.
Bring a heavy bottomed & oven proof pan (cast iron works best) to medium high heat.
Add enough vegetable oil to lightly coat the bottom of the pan. Turn your oven vent on – there may be a fair amount of smoke. Grab a splatter guard as well, if you’ve got one.
When the oil is hot, add the tenderloin and pan fry ~ 2 minutes on two sides (there are usually 3 sides for a tenderloin).
Flip the pork tenderloin to the third side and immediately transfer to an oven.
Cook 12-15 minutes or until internal temperature reaches 145F.
Tent loosely and let sit 10 minutes before slicing / serving
Add salt to taste. Happy eating! Beckie
Notes
You may need to sear the tenderloins in batches if the pan is not big enough. It's important to sear and not steam the meat.
The pork tenderloin will be easier to slice when the meat has cooled at least 15 minutes.