Combine sugar, cornstarch and salt in a heavy saucepan; stir well to remove lumps. Gradually add milk, stirring until blended. Cook over medium heat, stirring constantly, until mixture thickens and comes to a boil; cook 1 minute, stirring constantly. Remove mixture from heat.
Beat egg yolks until thick and lemon colored. Gradually stir about one-fourth of hot mixture into yolks; add to remaining hot mixture, stirring constantly. Cook over medium heat 2 minutes, stirring constantly. Remove from heat; add butter and vanilla; stir until butter melts. Gently stir in blueberries. Cool and pour into pastry shell. Beat whipping cream until foamy; gradually add powdered sugar, beating until soft peaks form. Spread over pie. Chill.
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