The night before roasting, put the the pork shoulder fat side up in a roasting pan, rub it all over with sage and salt, and then cover it and put it in the refrigerator overnight.
1-2 hours before you are going to start cooking, take it out of the refrigerator and let it sit on the counter to warm up a bit.
Preheat the oven to 300F.
Uncover the roast and put it in the oven.
Cook the roast for about 2 1/2 - 3 1/2 hours, or until the meat is mostly tender. (It will still be a little tough in the middle.) Check at 2 1/2 hours to see how it's doing, and then each 1/2 hour after.
Add the wine, 1 cup of water, the carrots and the parsnips. Cook for 1 hour.
Take the roast out of the oven and increase the temperature to 375F.
Break up the roast into smaller pieces, keeping the fat side up. Add more water if needed. Put the roast back in the oven and cook it for 15-20 minutes more. It should be browned and very tender when you take it out.
Scoop out the pork and the vegetables into a serving platter. Then skim the fat off the juices and pour them into a serving cup to be used at table.