Line 8-inch square pan with foil, with ends of foil extending over sides. Microwave white chocolate, 6 tablespoons butter and water in large microwaveable bowl on HIGH 2 minutes or until butter is melted; stir with whisk until chocolate is completely melted and mixture is well blended.
Add dry pudding mix; stir 2 minutes. 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 minutes 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.