Combine first 4 ingredients in a saucepan; stir in milk. Cook over medium heat, stirring constantly, until mixture comes to a boil. Reduce heat and simmer, stirring constantly, 2 minutes or until thick. Remove from heat. Cover surface of pudding with plastic wrap. Cool completely in refrigerator.
Gently fold whipped topping into peppermint mixture. Spoon into piecrust. Cover and chill at least 8 hours. Sprinkle with additional crushed peppermint candies.