In a small saucepan, combine the sugar, cornstarch and salt. Stir in milk until smooth. Cook and stir over medium-high heat until thickened and bubbly. Reduce heat; cook and stir 2 minutes longer. Remove from the heat.
Stir a small amount of hot filling into egg yolks; return all to the pan, stirring constantly. Bring to a gentle boil; cook and stir 2 minutes longer. Remove from the heat.
Gently stir in vanilla. Cool to room temperature without stirring. Transfer to a bowl; press plastic wrap onto surface of custard. Refrigerate for at least 1 hour.
Just before serving, spoon 1/4 cup of berries into each parfait glass; top with 2 tablespoons of custard. Repeat layers.