Step 1

Preheat oven to 325°F. Microwave semi-sweet and unsweetened chocolates and butter in large microwavable bowl on HIGH 2 to 3 minutes or until butter is melted, stirring after 2 minutes. Stir until chocolate is completely melted. Cool to room temperature.

Step 2

Beat eggs and granulated sugar in large bowl with electric mixer on medium speed until well blended. Add chocolate mixture and vanilla; mix well. Blend in flour, baking powder and salt. Add white chocolate chunks and walnuts; mix well. Drop heaping tablespoonfuls of dough, 2 inches apart, on greased baking sheets.

Step 3

Bake 10 minutes or until cookies are slightly cracked but still moist. Cool 2 minutes; remove from baking sheets. Cool completely on wire racks. Sprinkle evenly with powdered sugar.