Scrub the mussels under the faucet and remove the beards, and then set aside.
In a 6 quart saucepot place butter, flour, wine, lemon juice and clam juice and bring to a boil over high heat. Add the mussels and return to a boil. Reduce heat to low and simmer covered 3 minutes or until mussels are opened. With a slotted spoon remove mussels to 2 or 4 deep serving bowls or dishes and set aside.
Place the liquid into a blender or food processor and add the parsley, garlic cloves, shallot, salt and pepper and blend well. Pour the sauce over the mussels and serve with a French or Italian bread to sop up the wonderful sauce.