Heat the oven and prep the pork: Preheat the oven to 400°F. Pat the pork tenderloin completely dry with paper towels and trim off the thin silvery membrane running along one side, since it stays tough no matter how long it cooks.

Season it well: Stir together the salt, pepper, garlic powder, Italian seasoning, smoked paprika, and onion powder in a small bowl. Rub the pork all over with 1 tablespoon of the olive oil, then press the spice mixture into every side.

Sear all four sides: Heat the remaining 1 tablespoon olive oil in a large oven-safe skillet over medium-high heat until it shimmers. Sear the tenderloin for about 2 minutes per side, turning with tongs, 6 to 8 minutes total, until every surface is deeply browned.

Roast to 145°F: Slide the whole skillet into the oven and roast for 13 to 16 minutes, until an instant-read thermometer pushed into the thickest part registers 145°F. Start checking at 13 minutes; a thin tenderloin can get there fast.

Rest the meat: Move the pork to a cutting board, tent it loosely with foil, and let it rest at least 3 minutes (I give it 5 to 10). The USDA calls for 145°F plus a 3-minute rest, and that rest is also what keeps the juices in the meat instead of on your board.

Build the pan sauce: Set the skillet back over medium heat, using an oven mitt since the handle is still hot. Melt 1 tablespoon of the butter, add the garlic, and cook 30 seconds until fragrant. Pour in the chicken broth and whisk in the Dijon, scraping up the browned bits. Simmer 2 to 3 minutes until slightly reduced, then swirl in the remaining 2 tablespoons butter off the heat.

Slice and serve: Cut the tenderloin into 1/2-inch medallions, arrange them on a platter, and spoon the pan sauce over the top. Sprinkle with fresh parsley and serve warm.