Mix corn starch and remaining sugar in small saucepan. Stir in water and lemon juice; cook on medium heat 10 min. or until mixture is thickened and just comes to boil, stirring frequently. Add small amount to egg yolk in small bowl; stir until blended. Gradually stir into remaining lemon mixture in saucepan; cook 1 min. or until heated through, stirring constantly. Strain, if necessary. Cool slightly.