Cook potatoes until tender. Set aside in large bowl.
In Dutch oven over medium heat, fry bacon until crisp. Remove bacon from pan and set aside with potatoes.
In the same pan, add 2 Tablespoons butter to bacon drippings. When butter has melted, make the roux by adding flour and cooking on low heat for 3 to 4 minutes. Remove roux from pot and set aside.
Add the remaining butter to the pan and sauté onions and celery until softened. Remove to bowl with potatoes and bacon.
Return roux to pot and add seafood stock and juice from clams. Raise the heat to high and cook, stirring frequently for 6 to 8 minutes until thickened.
When thickened, add clams, potato mixture, seasonings, heavy cream and half and half. Simmer about 10 minutes. Serve with sourdough bread and butter.
This recipe makes a relatively thin soup. If a thicker soup is desired, thicken with flour/water mixture.