Preheat oven to 425°F (220°C).

Heat oil in skillet over medium heat. Add prosciutto and leeks and sauté for 3 minutes or until leeks are softened. Stir in mustard, cream and thyme. Bring to boil and boil until mixture is thick, about 1 minute.

Roll out half of puff pastry into a 10 x 12-inch (25 x 30-cm) rectangle. Spread leek mixture over, leaving 1-inch (2.5-cm) border on all sides. Brush all exposed pastry with beaten egg. Place pork on upper third of pastry tucking any thin ends under. Season pork with salt and pepper. Bring short ends of pastry up over the ends of the pork. Roll pork in pastry until fully enclosed, cutting off pastry excess. Place seam-side-down on cookie sheet and prick top. Brush pastry with egg.

Bake for 20 to 25 minutes or until golden brown.

Place port, orange juice and stock in a skillet. Bring to boil and boil until reduced down to 1 cup (250 mL). Stir in soy sauce and cream. Bring to boil and reduce until slightly thickened.

Slice pork into slices and drizzle with sauce.