Place the butter, onion and bacon in a large saucepan over medium heat and cook for 5-6 minutes or until soft and golden. Add the wine and cook for one minute. Add the bay leaf, tomatoes, stock and potato and simmer, covered for 35 minutes or until potato is very soft. Cool slightly.
Meanwhile, heat the water in a large, deep frying pan over high heat. Add the pipis, cover with a tight fitting lid and steam for 2-3 minutes or until the shells have opened.
Reserve 12 pipis for serving. Remove the flesh from the remaining shells, discarding any unopened pipis. Process the cooled soup in a blender in batches until smooth. Return to a clean pan, add the pipi meat, parsley and cream and heat gently for 5 minutes. To serve, pour into bowls and top with the reserved pipis.