Peel, wash, and dice potatoes, and cook in the vegetable stock for about 15-20 minutes until soft.
Peel onion and finely chop it up. Coarsley cube the bacon. Heat butter in a saucepan. Saute bacon and onions, and remove the cooking fat. Sprinkle flour on top and let it fry. Add milk and heavy cream to vegetable broth with the potatoes. Season with salt and pepper. Let it simmer for another 5 minutes. Blend or stir vigorously with a whisk.
Drain canned chopped clams in a sieve and reserve the liquid. Cut two-thirds of the clams into small pieces. Clean and rinse the spring onions, and finely chop it up. Add all clams, clam liquid, spring onions, and cranberries into the soup and let it sit for a few minutes. Season again with salt and pepper. Add some more cooked clams to soup according to taste. Garnish with chopped parsley and serve.
Tip: It is typical American custom to add saltine crackers or small oyster crackers to the soup.