Make roux by melting butter over medium-low heat in a 1 1/2 gallon heavy stockpot. Add onions and saute until translucent. Reduce heat to low, add flour, and stir to blend. Cook for 2 to 4 minutes over low heat, stirring frequently. Set aside to cool.

Make stock. In a separate pot, bring to a boil the clams and natural clam juice. Reduce the heat and let simmer for 15 to 20 minutes. In another large pot, cover potatoes with cold water. Bring to a boil and cook until soft. Drain and set aside.

Add the hot stock to the cooled roux and whisk thoroughly until smooth. Slowly bring to a boil. Reduce heat and add cooked potatoes. Whisk in half-and-half, being careful not to smash potatoes. Simmer for 5 to 10 minutes.

Serve in warm soup bowls and sprinkle with a dash of paprika