Melt butter in a large kettle or stock pot over medium heat. Add onions and saute until clear. Stir in flour and cook over low heat, stirring frequently, for 2 to 4 minutes. Set aside to cool.
In a separate pot, bring clams and clam juice to a boil. Reduce heat and simmer for 15 minutes.
In a small saucepan, cover peeled potatoes with water. Bring to a boil and cook until potatoes are tender, about 15 minutes. Drain and set aside.
Slowly pour hot clam stock into butter/flour mixture while stirring constantly. Continue stirring and slowly bring to a boil. Reduce heat and add cooked potatoes. Mix in half and half, salt and pepper and chopped dill. Heat through but do not boil.