Preheat and prep: Heat your oven to 400°F (205°C).
Pat the pork dry with paper towels to help it brown well.
Season generously: Sprinkle the tenderloin all over with 1 to 1.5 teaspoons kosher salt, 1 teaspoon black pepper, 1 teaspoon smoked paprika, and 1 teaspoon dried thyme. If using brown sugar, rub 1 teaspoon per tenderloin over the surface.
Mix a quick glaze: In a small bowl, combine 2 tablespoons softened butter, 1 teaspoon Dijon, and 1 minced garlic clove. Set aside.
Sear on the stovetop: Heat a large oven-safe skillet over medium-high.
Add 1 tablespoon oil. When shimmering, sear the pork on all sides until deep golden, about 6–8 minutes total.
Glaze and roast: Turn off the heat. Brush the top and sides of the pork with the butter mixture.
Transfer the skillet to the oven.
Roast to temp: Bake 10–14 minutes, depending on thickness, until the center reaches 140–145°F on an instant-read thermometer. Start checking at 10 minutes.
Rest the meat: Move the pork to a cutting board and tent loosely with foil for 5–8 minutes. The temperature will rise slightly as it rests.
Make a quick pan sauce: Return the skillet to medium heat.
Add 1/3 cup chicken broth and a small squeeze of lemon. Stir, scraping up brown bits. Simmer 2–3 minutes to reduce slightly.
Whisk in 1 tablespoon cold butter and the remaining minced garlic clove for a glossy finish. Taste and season with salt and pepper.
Slice and serve: Slice the tenderloin into 1/2-inch medallions, spoon over the pan sauce, and serve immediately.