In top of double boiler, set over pan of simmering water, melt unsweetened
chocolate and butter.
In bowl of electric mixer, beat eggs and sugars until thickened. Stir in butter
mixture.
In bowl, stir together flour, baking powder and salt. Gradually add flour
mixture to egg mixture, beating just until incorporated. Do not overbeat. Stir
in walnuts and chopped chocolate.
Scoop out batter by 1/4-cup measure onto ungreased cookie sheet, leaving 2
inches between cookies, about 6 cookies per sheet. Chill in refrigerator 1 hour.
Bake at 300 degrees 30 minutes until cookies are firm to the touch. Cool 2
minutes on cookie sheet, then remove to wire rack to cool completely.