How to Make It
In a large skillet, heat the olive oil until shimmering. Add the onion and cook over moderate heat until translucent, about 3 minutes. Add the sausage and cook, breaking it up with a wooden spoon, until cooked through, about 3 minutes. Add the apple, garlic, thyme and sage and cook until the apple just begins to soften, about 2 minutes. Stir in the collard greens and cook until wilted, about 2 minutes. Transfer the mixture to a medium bowl and let cool to room temperature. Mix in the goat cheese and season the stuffing with salt and pepper.
Light a grill. Using a long, thin knife and beginning at a thick end, cut a 1-inch-wide pocket through the center of each pork tenderloin; use the handle of a wooden spoon to widen the pocket if necessary. Fill the pork tenderloins with the stuffing, poking it in with the wooden spoon. Season the tenderloins with salt and pepper and wrap the bacon strips securely around them; try to cover any exposed stuffing with the bacon.
Grill the pork tenderloins over moderately high heat, turning four times, until browned on every side, about 25 minutes, or the internal temperature reaches 140°. Transfer the pork tenderloins to a cutting board, cover tightly with foil and let rest for 10 to 15 minutes.
In a medium saucepan, heat the oil. Add the garlic and cook over moderate heat until fragrant, about 1 minute. Add the apple, cider, Riesling, chicken stock, sage and thyme and simmer until the apple softens, about 7 minutes. Transfer the contents of the saucepan to a blender and puree until smooth. Strain the sauce back into the saucepan and boil until it coats the back of a spoon, about 5 minutes. Season with salt and pepper.
Slice the pork tenderloins crosswise about 1 inch thick and arrange on plates. Spoon the Apple-Riesling Sauce around the meat and serve.