Shells should be tightly closed or close when lightly tapped.  Clean just
before cooking.  To clean, scrub well to remove mud, seaweed and beard.
Rinse well.
Place mussels in a large kettle containing about 1/2 inch of water.  Bring to a
boil and steam mussels tightly covered until shells open, about 5 to 7
minutes.  Discard any unopened mussels.  Serve immediately with melted
butter for dipping.
For variety, steam mussels in the same amount of white wine, beer, or clam
juice as water in above directions.