HEAT oven to 350°F.
BLEND 2 cups nuts in blender until finely ground, using pulsing action. 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 whipping cream, powdered sugar and vanilla in saucepan on low heat just until chocolate is completely melted, stirring constantly. Pour over pie; spread to cover top of pie. Refrigerate 2 hours.