Rub the pork loin with a mixture of salt and pepper, the sugar and cayenne. Place it on a rack and roast for ten minutes.
Reduce the oven heat to slow (300°F.). Sprinkle the roast with rosemary and pour around it half of the wine. Continue to roast for two to two and one-half hours, basting frequently and adding more wine as necessary.
When done, remove the roast to a hot platter. Strain the juices from the pan into a saucepan. Skim off and discard fat. Bring to a boil and add the stock and butter. Serve the sauce separately.