In a large pot add 4 tbls butter
and onion, sauté. Don't let the onions brown.
Add the peeled and sliced potatoes, milk and stock.
Add the herbs. Cover and cook gently for about an hour.
Prepare the roux: melt the butter in a small
saucepan and whisk in the flour. Let the flour and butter mixture (the
roux) bubble for 2 minutes on medium-low heat, stirring constantly. Thicken the
soup with the roux, whisking to avoid lumps. Cook for 5 to 10 minutes and
then puree the soup in a food processor or blender.
Add the cream, do not boil. Season to taste with
salt and black pepper. If you like, top each bowl of soup with chopped
fresh chives.