Melt bittersweet chocolate chips and butter in a double boiler or microwave.
In a large bowl, beat eggs and sugar until thick. Stir in chocolate mixture.
In a separate bowl, combine flour and baking powder. Stir into chocolate mixture. Stir in semi-sweet chocolate chips and nuts.
Refrigerate dough for at least an hour, or until firm.
Preheat oven to 375°. Grease or line baking sheets and set aside.
Drop dough by tablespoonfuls onto baking sheets, leaving about 1 & 1/2 inches between cookies. Bake 12-14 minutes or until shiny crust forms on top but interior is still soft. Cool on baking sheets.
Makes about 24 cookies.