Preheat oven to 350 degrees.
Chop 8 squares of chocolate; set aside.
Microwave remaining 8 squares chocolate in large microwave safe bowl on high 2 minutes.
Stir until chocolate is melted and smooth.
Stir in sugar, butter, eggs, and vanilla with a wooden spoon until well blended.
Stir in flour and baking powder.
Stir in reserved chopped chocolate and nuts.
Drop by scant 1/4 cupfuls onto ungreased cookie sheets.
Bake for 13 to 14 minutes or until cookies are puffed and feel set to the touch.
Cool on cookie sheet 1 minute and remove to wire rack.
*Note: If omitting nuts, increase flour to 3/4 cup to prevent spreading.