1/2teaspoonchipotle chile powderfor less heat, substitute regular chili powder
Place a rack in the center of your oven and preheat the oven to 400 degrees F. With a sharp knife, cut away and discard the silver skin (tough membrane) from the pork.
In a small bowl, combine the paprika, brown sugar, salt, cumin, mustard, black pepper, and chipotle powder in a bowl.
Heat a cast-iron pan or similar oven-safe, heavy-bottomed pan over medium-high heat. Once the pan is hot, add the oil and let it warm up for another minute or two.
Coat the pork tenderloin on all sides with the spice rub.
Once the oil is hot, sear the pork on all sides (be careful to lower the pork into the pan away from you in case of oil splatters). You’ll need about 2 to 3 minutes per side—it can get a bit smoky, so turn on your fan (or open the windows if you don't have one). The pork should have a nice crust but not be all the way cooked through.
Transfer the pan to the oven. Bake the pork tenderloin until the internal temperature reaches 135 degrees F on an instant read thermometer, about 8 to 10 minutes. Transfer to a plate, cover, and let rest at least 10 minutes (pork is considered safe to eat at 145 degrees F, but its internal temperature will continue to rise as it rests). Slice the pork into 1-inch medallions. Serve warm, with pan juices spooned over the top.
If cooking 2 pork tenderloins, brown them one at a time, then nestle them into the skillet together to bake.
If you can only find a pork tenderloin that is already brined, rinse it off, pat it dry, and omit half of the salt from the rub
TO STORE: Refrigerate pork in an airtight storage container for up to 3 days.
TO REHEAT: Gently reheat leftovers in a small skillet or in the microwave.
TO FREEZE: Freeze pork in an airtight, freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.