Sherbet maybe frozen in half or whole lemons. For halves, cut larges lemons in half squeeze juice and scrape out all the pulp, using a grapefruit spoon. For whole lemons, cut a slice from the top, loosing the pulp with a grapefruit knife and scoop it out. Strain through a sieve, pressing the pulp to extract all the juice. Reserve juice. Place the lemon shells in cake pan, cover with a plastic wrap and refrigerate.
To prepare sherbet, combine 1 cup water and ¾ cup sugar and bring to boil in a saucepan. Simmer 5 minutes and let cool. Add salt, cream, juice and rind. Pour into freezer tray or shallow metal pan. Freeze until almost firm. Beat smooth with a mixer.
Beat egg whites to soft peaks, fold into lemon mixture thoroughly. Freeze again until firm enough to mound from a spoon. Spoon into lemon shells. Place in a cake pan, cover with a plastic wrap and freeze until firm.
Decorate with green leaves and drizzle sherbet with an orange liqueur if desired.