Pork today is so lean, the meat will be dry and crumbly if overcooked, but there are a couple of tricks to help avoid that fate. The first is to turn the pork over halfway through the cooking time so the juices will concentrate in the center of the roast instead of settling on the bottom. Second, take the roast out of the oven when it is about 5° below the recommended internal temperature, which is 160°F. The meat will continue to cook as it rests.
- Preheat oven to 400°F.
- Combine rosemary, garlic, 1/2 teaspoon salt and 1/2 teaspoon pepper in a mortar and crush with the pestle to form a paste. (Alternatively, finely chop the ingredients together on a cutting board.)
- Coat a large roasting pan with cooking spray. Place pork in the pan and rub the rosemary mixture all over it. Toss potatoes with 2 teaspoons oil and 1/4 teaspoon salt in a medium bowl; scatter along one side of the pork.
- Roast the pork and potatoes for 30 minutes. Meanwhile, toss squash with the remaining 2 teaspoons oil, 1/4 teaspoon salt and pepper in a medium bowl.
- Remove the roasting pan from the oven. Carefully turn the pork over. Scatter the squash along the other side of the pork.
- Roast the pork until an instant-read thermometer inserted in the center registers 155°F, 30 to 40 minutes more. Transfer the pork to a carving board; tent with foil and let stand for 10 to 15 minutes. If the vegetables are tender, transfer them to a bowl, cover and keep them warm. If not, continue roasting until they are browned and tender, 10 to 15 minutes more.
- After removing the vegetables, place the roasting pan over medium heat and add port (or prune juice); bring to a boil, stirring to scrape up any browned bits. Simmer for 2 minutes. Add broth and bring to a simmer. Simmer for a few minutes to intensify the flavor. Add any juices that have accumulated on the carving board.
- To serve, cut the strings from the pork and carve. Serve with the roasted vegetables and pan sauce.