In a medium sized saucepan; add milk and egg yolks, beat together with whisk. Turn heat to low.
In a small bowl, mix sugar, cornstarch and salt; add to the milk mixture.
Turn up the heat to medium, and constantly stir until the mixture comes to a low boil and thickens to a pudding consistency.
Remove from heat; pour into a bowl, and cover with wax paper pressed up against the pudding so that a skin doesn't form.
Cool in the refrigerator for several hours or until the pudding is no longer warm.
NOTE: This is a good time to pre-bake your crust so it's cooled and ready to go!
Once chilled, whip the pudding with a mixer until creamy; add peanut butter and vanilla, and beat until smooth.
Pour into a deep dish pie crust that has been pre-baked according to package instructions and cooled.
If desired, top with homemade whipped cream or Cool Whip.