1. Beat peanut butter, cream cheese and vanilla in medium bowl on medium speed of mixer until smooth. Gradually add powdered sugar and milk, beating until smooth. Fold in whipped topping.
2. Place 1 cup peanut butter mixture in separate bowl. Spread remaining mixture into crust.
2. Place chocolate chips in small microwave-safe bowl. Microwave at MEDIUM (50%) 30 seconds or until chocolate is melted and smooth when stirred. Stir chocolate into reserved peanut butter mixture, blending thoroughly; drop by tablespoons onto top of pie. Using knife or spatula, gently swirl for marbled effect.
3. Cover; freeze 3 to 4 hours or until firm. Garnish as desired. Makes 8 servings.