In a heavy saucepan, combine sugar, cornstarch, salt, egg yolks & milk. With a wire whisk, beat ingredients until very well blended. Cook over medium high heat, stirring constantly until mixture is very thick. (I used a heavy 2 qt. saucepan & it took about 8-10 minutes to thicken). Remove from heat, add butter and vanilla. Stir in crushed pineapple. Add 1 cup of Cool Whip while mixture is hot. Pour into prepared crust. Top with sweetened whipped cream or cool whip. Refrigerate.