Chill a 2-quart mold and line quickly with sherbet.
Put in freezer.
Whip cream until stiff.
Add sugar, vanilla, and liqueur.
Force enough berries through sieve to make 1 cup, and add to cream.
Fill center of mold with cream mixture and freeze until firm.
Unmold on serving plate.
Decorate with fresh berries and whipped cream, if desired.
Makes 6 to 8 servings.