- 2 large sweet-tart apples, such as Fuji or Braeburn, sliced
- 1 large bulb fennel, trimmed, cored and thinly sliced
- 1 large red onion, sliced
- 5 teaspoons canola oil, divided
- 1 pound pork tenderloin, trimmed
- 1 teaspoon kosher salt
- 1/4 teaspoon freshly ground pepper
- 3 tablespoons cider vinegar
- 1 tablespoon chopped fennel fronds
- Position racks in upper and lower thirds of oven; preheat to 475 degrees F.
- Toss apples, sliced fennel and onion with 1 tablespoon oil in a large bowl. Spread out on a rimmed baking sheet. Roast on the lower oven rack, stirring twice, until tender and golden, 30 to 35 minutes.
- About 10 minutes after the apple mixture goes into the oven, sprinkle pork with salt and pepper. Heat the remaining 2 teaspoons oil in a large ovenproof skillet over medium-high heat. Sear the pork on one side, about 2 minutes. Turn the pork over and transfer the pan to the top oven rack. Roast until just barely pink in the center and an instant-read thermometer registers 145 degrees F, 12 to 14 minutes.
- Transfer the pork to a cutting board and let rest for 5 minutes. Immediately stir vinegar into the pan (be careful, the handle will be hot), scraping up any browned bits, then add to the apple mixture. Thinly slice the pork; serve with the apple mixture and sprinkle with fennel fronds.