HEAT oven to 325ºF.
MICROWAVE first 3 ingredients in large microwaveable bowl on MEDIUM 1 to 2 min. or until butter is melted. Stir until chocolates are completely melted and mixture is well blended. Stir in sugar. Blend in eggs and vanilla. Add flour and baking powder; mix well. Stir in nuts.
DROP by rounded tablespoonfuls, 1/2 inch apart, onto baking sheets.
BAKE 12 min. or until centres are set. (Do not overbake.) Cool 5 min. on baking sheets; remove to wire racks. Cool completely.