Makes: 10 servings. Prep: 15 minutes. Cook: about 35 minutes.
1. Remove the muscle on the side of the scallop that it uses to attach itself to the shell and discard. Refrigerate the scallops and clams until ready to use.
2. Melt butter in a large soup pot over medium-low heat. Add the leeks and gently cook them until softened, about 3 minutes. Add the flour and cook, stirring constantly, for 2 minutes longer. Add wine and clam juice. Increase heat to medium-high; boil until reduced by a third, about 15 minutes. Add cream and potatoes; return heat to medium-low. Simmer until potatoes are tender, about 12 minutes. (Can be made ahead to this point and chilled. To serve, reheat gently over low heat and proceed.)
3. Add the clams and scallops and simmer until just heated through, 2 to 3 minutes. Season with salt and pepper. Ladle into hot soup bowls and garnish with the parsley and paprika.