HEAT oven to 350°F.
USE pulsing action to blend 2 cups nuts in blender until finely ground. Mix with granulated sugar and butter; press onto bottom and up side of 9-inch pie plate. Bake 12 to 15 min. or until lightly browned. (If crust puffs up during baking, gently press down with back of spoon.) Cool completely.
MICROWAVE caramels and 1/3 cup whipping cream in microwaveable bowl on HIGH 2-1/2 to 3 min. or until caramels are completely melted and mixture is well blended, stirring after each minute. Pour into crust. Chop remaining nuts; sprinkle over caramel layer.
COOK chocolate, remaining cream, powdered sugar and vanilla in saucepan on low heat just until chocolate is completely melted and mixture is well blended, stirring constantly. Pour over pie; spread to cover top of pie. Refrigerate 2 hours.