In saucepan, place cubed potatoes and enough water to cover potatoes. Bring to a boil and cook just until tender. (Do not over cook) Meanwhile, in a separate saucepan, sauté diced celery, onions and garlic in butter. Add flour a little at a time, while stirring w/ wire whisk to soak up butter. While continuing to stir w/ whisk; add ½ & ½, then add clams and potatoes w/ water that they boiled in. Cook stirring constantly. Add milk if needed to thin. Salt and pepper to taste. Bring to a boil, thin or thicken as needed. Simmer 10-15 min.