Preheat oven to 350-375°F (180-190°C).

Season pork with salt and pepper. Pour oil into roasting pan, add pork and brush with oil. Place onion and carrots around pork and season with salt and pepper. Roast until cooked - juices should run clear when pierced with skewer - about 11/2 to 2 hours (time depends on thickness of pork). Add stock to pan after 20 minutes, and replenish with water during latter stage of cooking to keep vegetables moist. Turn pork during roasting to brown evenly.

Add 1 cup of water to boil in a sauce pan. When boiling, add julienne strips of rind from 1 orange. Cook for 3 minutes at medium heat. Remove the julienne strips of orange and keep them on the side for later use.

Add the slices from 2 oranges (segment) to the hot water and cook for 3 minutes at medium heat.

Drain them and keep the orange slices on the side for use later. Discard the water.

When pork is cooked, remove to serving platter, cover with foil and let stand in warm place. Skim excess fat from roasting pan contents and puree contents in blender, food mill or food processor. Pour into small pan and stir in combined cornstarch and sherry. Heat, stirring constantly, until slightly thickened and boiling gently. Add orange peel, segments, and heat gently 5 minutes.

To serve, carve pork into thin slices and spoon over orange sauce.