Preheat oven to 550°F. Spread rock salt in shallow baking dish in a layer about ¾ inch thick. Place prawns or shrimp in single layer, on their sides, directly onto salt, pressing them down slightly to burry. Roast until prawns are barely pink, 5-7 minutes. Remove from oven, and let prawns stand in salt in baking dish about 5 minutes. Nestle aioli bowl in center of baking dish surrounded by salt and prawns.