Prepare and bake Piecrust in a 9-inch pie plate. Cool completely on a wire rack.
Combine raisins and rum in a small microwave-safe bowl; microwave at HIGH for 1 minute or until raisins are plump. Set aside.
Combine the sugar, cornstarch, salt, and eggs in a large bowl, and stir well with a whisk.
Heat milk over medium-high heat in a small, heavy saucepan to 180° or until tiny bubbles form around edge (do not boil). Gradually add hot milk to sugar mixture, stirring constantly with a whisk. Place mixture in pan; cook over medium heat until thick and bubbly (about 10 minutes), stirring constantly. Remove from heat; stir in butter.
Spoon custard into a bowl; place bowl in a large ice-filled bowl for 10 minutes or until custard comes to room temperature, stirring occasionally. Remove bowl from ice. Stir in raisins and vanilla; spoon mixture into prepared crust. Spread whipped topping evenly over filling. Loosely cover and chill 8 hours or until firm.