Preheat oven to 450 F. Place piecrust in 9-in pie plate; bake as label directs for one crust pie shell.
In a 4 quart saucepan, stir together sugar, cornstarch, and salt. In a large bowl whisk milk and egg yolks until well blended, gradually whisk into sugar mixture. Heat on medium heat 6 to 7 minutes or until mixture thickens and boils, stiring constantly. Remove from heat: stir in peanut butter and vanilla until well blended
Immediately pour peanut butter mixture into the baked pie shell, press platic wrap onto surface of filling. Refrigerate pie at least 4 hours or until well chilled and set.
To serve top with whipped cream and garnish with chopped nuts.