1. Heat a 6- to 8-quart stockpot, add the butter and onion, and cook gently. Do not let the onion brown. Add the peeled and sliced potatoes, milk, and stock. Add the herbs. Cover and cook gently for about an hour.
2. Thicken the soup with the roux, whisking carefully to avoid lumps. Cook for 5 to 10 minutes and then puree the soup in a food processor or food blender.
3. Add the cream and gently reheat, but do not boil. Season with the salt and pepper. Serve with chopped fresh chives and the crisply fried bacon as garnishes.
PREPARE A ROUX:
1. Melt the butter in a small saucepan and whisk in the flour. Let the flour and butter mixture (roux) bubble for 2 minutes on medium-low heat, stirring constantly.
TIP:
This soup can also be made with the chopped white part of 5 or 6 large leeks instead of onions. Additional garnishes you can use instead of bacon are chopped prawns or a small dice of lobster.
