Preheat and prep. Heat your oven to 400°F (205°C).
Pat the pork dry with paper towels. Dry meat sears better and gets a nicer crust.
Make the herb paste. In a small bowl, mix olive oil, garlic, rosemary, thyme, parsley, Dijon, salt, pepper, lemon zest, and lemon juice. If you like a bit of heat, add red pepper flakes.
Season the pork. Rub the herb paste all over the tenderloins.
Press it in so it sticks. Let it sit on the counter for 10–15 minutes while you heat your pan.
Sear for color. Heat a large oven-safe skillet (cast iron is ideal) over medium-high. Add a thin film of olive oil.
When the oil shimmers, add the pork. Sear 2–3 minutes per side until nicely browned.
Roast to finish. Transfer the skillet to the oven. Roast 12–18 minutes, depending on thickness, until a thermometer inserted in the thickest part reads 140–145°F (60–63°C).
The temperature will rise slightly as it rests.
Rest the meat. Move the tenderloins to a cutting board and tent loosely with foil. Rest 8–10 minutes to keep the juices in.
Make a quick pan sauce. Place the hot skillet over medium heat. Add the broth or wine to deglaze, scraping up the browned bits.
Simmer 2–3 minutes to reduce slightly. Whisk in the butter until glossy. Taste and adjust salt and pepper.
Slice and serve. Slice the pork into 1/2-inch medallions.
Spoon the pan sauce over the top and sprinkle with fresh parsley. Serve with your favorite sides.