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. Prepare A Rous: Melt The Butter In A Small Saucepan And Whisk In The Flour. Let The Mixture Bubble For 2 Minutes On Med-Low Heat, Stirring Constantly. Thicken The Soup With The Roux, Whisking Carefully To Avoid Lumps. Cook For 5 To 10 Minutes And Then Puree The Soup. Add The Cream And Gently Reheat, But Do Not Boil. Season With The Salt And Pepper. Serve With Garnishes.