In top of double boiler, or carefully in saucepan over low heat, combine the sugar, cornstarch, chocolate and salt; mix well.

Then gradually stir in the milk.

Cook, over boiling water, stirring, until the mixture is thickened, about 10 minutes.

Cook, covered, stirring occasionally, 10 minutes longer.

Gradually stir half of the hot mixture into beaten egg yolks. Return to rest of mixture in double boiler; cook over boiling water, stirring occasionally, 5 minutes.

Remove from heat; stir in vanilla. Pour chocolate filling into baked pie shell.

Refrigerate until well chilled, at least 3 hours. If desired, put piece of wax paper over top of pie so a film does not form on it.