Filling:
1 cup oyster mushrooms, chopped
3/4 cup Fuji apples, chopped
1 pound kale, bottom stems trimmed
2 teaspoons kosher salt plus more
2 tablespoons unsalted butter
1 cup minced onion
1 tablespoon finely minced garlic
1 1/2 teaspoons dried thyme
1 1/2 teaspoons dried rosemary
2 tablespoons rye bourbon
1/2 teaspoon freshly ground black pepper
1 pound ground pork
Pork:
1 (trimmed) 2 1/2–3 pound pork loin
1 teaspoon kosher salt plus more for seasoning
1/2 teaspoon freshly ground black pepper plus more for seasoning
3 ounces thinly sliced prosciutto
5 sprigs rosemary
4 medium Fuji apples, halved
3 tablespoons unsalted butter, divided
2 tablespoons extra-virgin olive oil
1 cup dry hard cider
1/2 cup low-salt chicken stock
1 | Place mushrooms and apples in separate small bowls. Meanwhile, blanch kale in boiling salted water just until wilted, about 1 minute. Using tongs, transfer kale to a rimmed baking sheet. Refrigerate until cool. Remove any large, tough ribs.
2 | Melt butter in a large skillet over medium heat. Add onion; cook, stirring often, until soft and lightly golden, about 8 minutes. Add mushrooms and apples; cook, stirring occasionally, until flavors meld, about 5 minutes. Stir in garlic, thyme, and rosemary; cook for 1 minute. Add bourbon and cook until liquid is absorbed, about 1 minute. Stir in 2 teaspoons salt and 1/2 teaspoon pepper. Transfer mixture to a bowl and let cool completely. Add ground pork and stir to combine well.
For pork:
1 | To butterfly, put pork loin on a work surface with short end facing you. Holding a long, thin sharp knife parallel to work surface and beginning along one long side, cut 1/2" above underside of roast. Continue slicing inward, pulling back the meat with your free hand and unrolling the roast like a carpet, until the entire loin is flat. Cover with a sheet of plastic wrap. Using a meat mallet, pound to an even thickness.
2 | Uncover pork. Season with 1 teaspoon salt and 1/2 teaspoon pepper. Place kale leaves on top of loin in an even layer, overlapping as needed and leaving a 1" border. Spread filling on top of kale. Roll pork into a tight cylinder. Wrap one layer of prosciutto around roast. Tie roast securely with kitchen twine in 1" intervals. Tuck rosemary sprigs under twine, spacing apart. DO AHEAD: Pork roast can be made 1 day ahead. Cover and chill. Let stand at room temperature for 1 hour before continuing.
3 | Preheat oven to 400°F. Place apples in a roasting pan. Melt 1 tablespoon butter with oil in a large skillet. Brown pork on all sides, about 5 minutes total, then set on top of apples in pan. Add cider and 1/2 cup water to skillet and bring to a boil, scraping up browned bits. Pour mixture into roasting pan. Roast pork until an instant-read thermometer inserted into center of loin registers 140°F (it will be cooked medium but still slightly pink), about 1 hour 40 minutes. Let roast rest for at least 20 minutes and up to 2 hours.
