LINE 8-inch square pan with foil, with ends of foil extending over sides. Microwave white chocolate, 6 Tbsp. butter and water in large microwaveable bowl on HIGH 2 min. or until butter is melted; stir with whisk until chocolate is completely melted and mixture is well blended.
ADD dry pudding mix; stir 2 min. Add sugar, 1 cup at a time, stirring after each addition until well blended. Press onto bottom of prepared pan.
MICROWAVE semi-sweet chocolate and remaining butter in large microwaveable bowl 1-1/2 min. or until butter is melted. Stir until chocolate is completely melted and mixture is well blended; spread over fudge layer in pan. Sprinkle with nuts. Refrigerate 2 hours or until firm before cutting into 36 squares.
Storage Know-How: Store cut-up fudge between sheets of waxed paper in airtight container in refrigerator up to 2 weeks.
Chocolate-Banana Fudge: Prepare as directed, using JELL-O Banana Cream Flavor Instant Pudding and substituting chopped banana chips for the pistachios.