8 cups chicken stock
6 russet potatoes, peeled and cut into large pieces
4 leeks (whites only), thoroughly washed and sliced
3 stalks celery, roughly chopped
1 bay leaf
1 1/2 teaspoons finely chopped fresh thyme
Salt and freshly ground pepper
1 cup heavy cream
Put the chicken stock, potatoes, leeks, celery, bay leaf and thyme in a large pot and sprinkle with salt and pepper. Boil until the potatoes are soft, 15 to 20 minutes.
Remove the bay leaf. Using an immersion blender (or in batches in a blender or food processor), blend the soup until smooth. Pour the soup into a medium pot; add the cream and simmer until the soup has thickened, about 20 minutes.