Preheat the oven. Preheat oven to 425°F (218ºC). Lightly grease a 9x13-inch baking dish.
Prep the pork. Pat the pork tenderloins (2) thoroughly dry with paper towels. Trim away any silver skin.
Make the Dijon seasoning. In a small bowl, stir together the Dijon mustard (3 tablespoons), olive oil (2 tablespoons), brown sugar (2 tablespoons), sweet paprika (1 teaspoon), garlic powder (1 1/2 teaspoons), onion powder (1 teaspoon), thyme (1 teaspoon), salt (1 1/2 teaspoons), and black pepper (3/4 teaspoon) until evenly combined.
Season the tenderloins. Place the pork in the prepared baking dish, leaving some space between the tenderloins. Rub the Dijon mixture evenly over all sides of the pork.
Add the butter. Divide the butter pieces (4) evenly over the tops of the tenderloins.
Bake. Bake, uncovered, for 20–30 minutes, or until an instant-read thermometer inserted into the thickest part of each tenderloin registers 145°F (63ºC). Begin checking early since cooking time will vary depending on the thickness and weight of the tenderloins.
Rest the pork. Transfer the tenderloins to a cutting board and loosely tent with foil. Let rest for 5–10 minutes before slicing.
Finish the pan juices. While the pork rests, stir the melted butter, pork drippings, and seasonings remaining in the baking dish until well combined.
Slice and serve. Cut the pork crosswise into slices and spoon the warm buttery Dijon pan juices over the top.