Wash the clams under cold running water.
Simmer the onion, leek, carrot, parsley, and thyme in 400ml of water for 10 minutes.
Add the wine, bring to a boil, then add clams and cook covered until they open.
Drain the mixture into a colander and reserve the flavored cooking liquid.
Remove clams from shells and combine the meat and vegetables with the reserved broth.
Sauté the chopped onion in butter until transparent.
Add 250ml of stock and bring to a simmer.
Add sliced potatoes and simmer until they are tender.
Purée half of the potato mixture in a blender until smooth.
Reheat the combined potato mixtures, clams, broth, and cream.
Season to taste and serve garnished with chopped parsley and whipped cream.