Melt half of the chopped chocolate with the butter in the top of a double boiler over simmering water. Let cool.
Mix in the sugar, eggs and vanilla. In a small bowl, sift the flour, baking powder and salt. Stir the dry ingredients into the melted chocolate mixture. Stir in the remaining chopped chocolate and the nuts. Cover the mixture and refrigerate for 1 hour.
Lightly butter two large baking sheets. Drop the batter in 2-tablespoon measures per cookie. Press down gently on each cookie. Bake until they’re just starting to crack, 12 to 13 minutes.
Cool the cookies completely on the sheet. Remove and store in a cookie jar, or place in the freezer and serve cold. Makes Two Dozen