Apple, Sage, and Prosciutto-Stuffed Pork Loin

Preheat oven to 375 degrees F. In large, ovenproof skillet over medium-high heat, heat 2 tablespoons olive oil. Cook apple and onion until beginning to soften, 4 minutes. Add garlic and sage and cook 2 minutes more. Season with salt and pepper. Transfer to bowl and let cool slightly. Butterfly pork loin: Using sharp knife, make slit lengthwise down center of pork, cutting it in half so it opens like a book (don’t cut it all the way through; it should still be attached at the bottom.) Season inside with salt and pepper and top cut-side of pork with prosciutto and apple filling. Pull two sides of pork around filling and tie tightly with kitchen string. (We used 4 pieces of string to tie pork in 4 places and trimmed off ends.) In same skillet, heat 2 more tablespoons olive oil over medium-high heat. Add pork and sear 6 minutes, turning every 1 to 2 minutes or so, until browned. Place entire skillet in oven and roast 20 minutes, or until internal temperature reaches 145 degrees F. Remove from oven and transfer to cutting board; cover with aluminum foil and let sit 10 minutes. Meanwhile, in separate large skillet, heat remaining 2 tablespoons olive oil over medium-high heat and cook garlic until fragrant, 2 minutes. Add half spinach and cook until wilted, about 4 minutes. Add remaining spinach and continue cooking until wilted. Season with lemon juice, salt, and pepper, and place in strainer to remove extra water. Slice pork and serve with spinach.