1 Preheat oven to 450°F.
2 How to butterfly the pork loin: Place the pork loin roast fat side down on a cutting board. Note that one long side of the pork loin roast will be thicker, and one side thinner.
Using a sharp knife, make a long cut an inch or so from the edge from the thinner long side of the roast at about a 45° degree angle, stopping a half inch from reaching the bottom of the roast.
Then angle the knife so that it is flat, parallel to the cutting board, and make slow, shallow cuts into the roast, along the same line.
As you cut, you can open up the top part of the roast like a book. Keep making slow, even cuts until you have "rolled" the roast out completely.
3 Pound the butterflied roast to an even thickness: With the pork roast unfolded, cover with 2 layers of of plastic wrap.
Pound with a meat mallet to flatten to a somewhat even thickness. Remove plastic wrap. Sprinkle the pork with salt and pepper and set aside.
4 Make the filling: Place the panko and stock in a small bowl and stir to combine.
Stir in the apples, walnuts, cranberries, shallots, maple syrup and rosemary.
5 Roll up pork roast with filling: Spread the filling over surface of the pork, leaving an inch margin around all sides except for the fat layer side—with that side leave a 2-inch margin.
Starting with the end of the roast rectangle that does not have the fat layer on the bottom, roll up the roast.
6 Secure with kitchen string. Tie the roast in 1 to 2 inch intervals with cotton kitchen string.
At this point you can wrap in plastic wrap and refrigerate if you are making ahead.
7 Bake: Coat the bottom of a roasting pan with cooking spray or a little olive oil. Place the roast in the pan and cook at 450°F for 15 minutes to brown the top, then reduce the oven temperature to 325°F. Cook uncovered, for about 30 to 40 minutes, or until the pork reaches an internal temperature of 140°F.
8 Rest and serve: Tent the roast with foil and let it rest for 10 minutes. Remove the kitchen string and slice into 1/2-inch thick slices to serve.
Save the pan drippings! Serve with pan drippings or use the pan drippings to make gravy. See How to Make Gravy.