Cider-Glazed Pork

Preheat oven to 400°. Whisk together cider, cider vinegar, and mustard in a small bowl and set aside. Trim any excess fat or silver skin from the tenderloin. Pat the pork dry with paper towels and season with salt, pepper and rosemary. In a large ovenproof skillet, heat 1 tablespoon butter and oil together over medium-high heat. Add the pork and sear until the bottom develops a golden-brown crust. Turn with tongs and continue to brown all sides, about 4 minutes more. Transfer pan to the oven. Roast until an instant-read thermometer registers 140°; 12 to 15 minutes, depending on the thickness of the meat. (The pork will continue to cook when it’s basted in the cider sauce.) Remove the skillet from the oven and transfer the pork to a clean plate to rest. Place the skillet over medium-high heat. Add the cider-mustard mixture and scrape up the browned bits on the bottom of the pan with a wooden spoon, then add remaining 2 tablespoons butter. Bring to a simmer then return the pork to the skillet. Spoon the cider mixture onto the pork by carefully tilting the skillet so that the liquid pools in the bottom of the pan. Continue to spoon the sauce onto the pork until the liquid reduces and thickens, about 2 minutes more. Let rest for 5 to 10 minutes before slicing. Cut the pork into slices and drizzle with more sauce. Serve warm.