Unroll the pork loin, opening out with a knife if necessary. Season with crushed garlic, salt and pepper. Drizzle with the wine and let rest in the fridge 4 hours.
Preheat oven to 180 degrees C. Drain the loin from the wine, sprinkle with basil, and evenly lay in the sliced prosciutto and black olives. Roll up like a Swiss roll and tie with string. Place on a baking tray and drizzle with olive oil.
Bake 1 hour or until tender. While cooking, turn occasionally so it browns evenly and baste with the pan juices.
While the pork cooks, make the walnut sauce. Dampen the bread with cold water and squeeze out the liquid. Place in a blender and add all sauce ingredients except the olive oil.
Blend until smooth. On low speed, gradually add the oil to form a creamy sauce.
Remove the pork from the oven and place on a serving platter. Serve the sauce in a gravy boat.