Combine 3 egg yolks and milk in saucepan. Blend well. Combine, sugar, cornstarch and salt. Stir into egg mixture. Cook stirring constantly until thick like pudding. Pour hot filling into bowl. Cover with waxed paper and chill. Whip chilled mixture with electric mixture until creamy. Add peanut butter and vanilla, beating until smooth. Pour filling into pastry shell. Cool whip on top.