Mix flour, baking powder and salt in medium bowl; set aside.
Beat together butter and sugar in large bowl until light and fluffy. Add eggs and vanilla; beat well. Stir in melted chocolate. Gradually beat in flour mixture. Sir in chocolate chunks and nuts. Drop by heaping tablespoonfuls onto ungreased cookie sheets.
Bake 11 to 12 minutes or until cookies feel set to the touch. Cool on cookie sheets 1 minute. Remove to wire racks and cool completely.