Preheat oven to 350ºF.
Coarsely chop 1 pkg (8 squares) of the chocolate. Set aside.
Microwave remaining 8 squares chocolate in large microwavable bowl on high for 2 minutes. Stir until chocolate is melted and smooth. Stir in sugar, butter, eggs, and vanilla until well blended. Stir in flour and baking powder. Stir in reserved chopped chocolate and nuts. Drop by large tablespoonfuls onto ungreased baking sheet about 2” apart. Bake for 13-14 minutes or until cookies are puffed, and feel set to the touch. Cool on cookie sheets for 1 minute before removing them to wire rack to finish cooling.