In a heavy large saucepan, combine sugar, tapioca, and salt. Stir in milk and let stand for 5 minutes. Meanwhile, beat egg yolks slightly. Stir yolks into tapioca mixture. Bring to a full boil, stirring constantly. Remove from heat. Stir in vanilla. Beat egg whites until stiff peaks form. Put 1/3 of the whites into a large bowl. Slowly stir in the tapioca mixture. Fold in remaining egg whites, leaving little fluffs of unblended egg white. Cover and chill. Serve topped with whipped cream or fruit.