One hour before serving, scrub 6 dozen softshell clams with vegetable brush in cold water; rinse with water until free of sand. Place clams in steamer or on rack in large kettle with 1 cup boiling water (or enough to cover bottom). Cover kettle with tight-fitting lid and steam over low heat just until clams open, about 5 to 10 minutes. Serve clams in soup bowls with individual cups of butter. Pour broth into mugs and sprinkle with a little chopped parsley. To eat: With fingers, pull clams from shells by the neck; dip first in broth to remove any sand, then into butter. Everything except the tough skin of the neck may be eaten. The broth can be drunk when the sand settles to the bottom.