Step 1

Arrange a rack in the middle of the oven and heat to 400°F.

Step 2

Whisk together the honey, vinegar, mustard, and cayenne in a small bowl; set aside.

Step 3

Trim any silver skin from the tenderloin. Turn under the tapered end and tie it in place with kitchen twine, or leave it loose to create a portion that will be very well-done. Pat the pork dry with paper towels and sprinkle generously with the measured salt and pepper.

Step 4

Heat the butter and oil in a large, ovenproof skillet over medium-high heat. Add the pork and cook until well-browned on all sides, turning with tongs, about 5 minutes total.

Step 5

Place in the oven to roast until an instant-read thermometer inserted horizontally into the end of the pork registers 140°F, about 12 minutes. Remove the skillet from the oven and transfer the pork to a clean plate.

Step 6

Place the skillet over medium-high heat. Pour the honey mixture into the skillet and stir to loosen any browned bits. When the liquid begins to sizzle, return the pork and any juices to the skillet. Gently tilt the skillet so that the liquid pools on one side of the pan and continuously spoon it over the top of the pork until the liquid thickens into a syrupy glaze, about 2 minutes. Transfer the pork to a serving platter and pour the glaze over the top. Let rest for 5 minutes. The internal temperature of the pork will rise to 145°F to 150°F.

Step 7

Cut the pork crosswise into slices. Drizzle with more honey and sprinkle with salt, pepper, and rosemary if using. Serve warm.