Combine tapioca, milk, egg yolk and 3 Tbsp. sugar in 1-1/2-qt. microwaveable bowl. Let stand 5 min. Beat egg white in small bowl with mixer on high speed until foamy. Gradually add remaining sugar, beating constantly until soft peaks form. Microwave on HIGH 7 to 8 min. or until mixture comes to full bowl, stirring every 2 min. Quickly stir egg white mixture into hot tapioca until well blended. Stir in vanilla. Cool 20 min. Stir before serving.