Roasting boneless pork is a lot easier than cooking many other types of meat. The layer of fat on the joint will help keep the meat moist, even with a long cooking time. All sorts of herbs go well with roast pork, as do traditional side dishes of vegetables and roast potatoes.
Preheat the oven to 230C. Place the oven rack in the middle so the roast will cook evenly.
Leave the layer of fat on one side of the pork in place. This fat will keep the meat moist, which is just what you want. Place the meat fat layer up. Doing this will allow the grease to drip down over the meat as it cooks. This will ensure the pork loin stays tender and does not dry out.
Create a rub with herbs, olive oil, and a little salt and pepper. About 1 tbsp of olive oil mixed with 1 tbsp of mixed spices is good. Oregano, rosemary, sage, thyme, and others are all great to use. If you like one more than another then create your own mixture based on your tastes. Rub the oil on the joint on both sides, giving it a good coating.
Place the joint in a roasting pan. Make sure you place the fat side up. If you don't have a roasting pan then you may place the loin on some rolled up tin foil to make a rack. You just don't want the loin resting in the pan. Now place the loin in a preheated oven. Cook at 230C for 10 minutes.
Turn the oven down to 120C. Now, cook from 45 minutes to 80 minutes depending on the size of your roast. When the meat thermometer reads 66C you know the roast is done. Cover the roast with aluminium foil and place it on the counter to cool for 15 minutes. Then, slice and serve with vegetables.
Serve the juice in the bottom of the pan as gravy.
Only rely on the thermometer to determine when the pork roast is done.