In medium saucepan, gradually whisk sugar into egg yolks and continue beating 3-4 minutes until mixture is slightly thick and pale yellow. Whisk in cornstarch. While beating the yolk mixture, gradually add the boiling milk in a thin stream. Place saucepan over moderate heat and stir continuously with a wooden spoon until the sauce thickens enough to coat the spoon. Remove pan from heat and continue to stir for several minutes before adding vanilla. Cover and chill. Serve over fresh fruit (strawberries, peaches, raspberries). Makes 2 cups.