Stir egg yolks lightly in medium-size bowl
. Stir in small amount of milk mixture. Slowy pour yolk mixture back into milk mixture, stirring with wire whisk to prevent lumping. Return saucepan to heat. Cook over low heat, stirring constantly, for about 2 minutes or until mixture is very thick; do not let boil. Remove saucepan from heat. Add chocolate
and stir until chocolate is melted. Pour filling into cooled crust. Place plastic wrap directly on surface of filling. Refrigerate for 2 hours or until the filling is thoroughly chilled.