Place a cast iron skillet on the middle rack of the oven and preheat to 450°F (230°C). Allow the skillet to heat with the oven. Once preheated, carefully remove the hot skillet, add the olive oil, and swirl to coat the bottom.
In a small bowl, mix the Italian seasoning, salt, black pepper, and garlic powder. Sprinkle the seasoning evenly over the pork and rub it in with your fingers to coat the meat. Place the pork in the prepared skillet.
Using oven mitts, return the skillet to the oven and bake for 10 minutes.
Remove the skillet from the oven, flip the pork using tongs, lower the oven temperature to 400°F (200°C), and return the skillet to the oven. Roast for an additional 15 minutes.
Remove the skillet from the oven and add the butter to the pan. Cover the skillet with a plate, pan lid, or foil and let the pork rest for 15 minutes. The pork is done when the internal temperature reaches 145°F in the thickest part.
Uncover the skillet and spoon the melted butter sauce over the pork.
Transfer the pork to a plate, slice, and spoon additional sauce over the top.
Notes
Season Evenly: Coat all sides of the pork tenderloin with the seasoning so every bite is well flavored. This helps create a more evenly seasoned, juicy pork tenderloin.
Trim Only if Needed: Most pork tenderloins are already trimmed. If you see any large pieces of surface fat or silver skin, remove them with a sharp knife before cooking.
Use the Butter Sauce: Adding butter after baking creates a simple pan sauce as it melts with the pork juices. Be sure to spoon the sauce over the pork before serving.
Rest Before Slicing: Cover the pork and let it rest for 15 minutes. Resting allows the juices to redistribute, keeping the pork tender and juicy when sliced.