Pork tenderloin is a boon for cooks in a hurry. While the meat cooks, make a packaged rice pilaf and some frozen vegetables.
Heat oven to 425 F.
Heat a well-seasoned cast-iron skillet over medium-high heat. (A lighter pan won't work.) Prep the pork, removing the membrane and any fat with a sharp knife. Fold tapered end back over tenderloin and tie it with kitchen string for uniform thickness. Dry with paper towels.
Grease hot skillet lightly. Brown pork on one side for about 3 minutes (don't move it around in the pan). Turn tenderloin over and put skillet in hot oven.
Remove meat after 20 minutes and check for doneness: 145 F on an instant-read thermometer, or a firm feeling when you poke the meat with a finger.
Transfer pork to a cutting board and make a simple, au jus-style sauce: Put skillet on high heat and deglaze with wine, fruit juice or broth, scraping up browned bits with a spatula or wooden spoon.