Preheat the oven to 175 degrees Celsius. Line baking sheets with parchment paper.
Melt the chocolate. Beat the egg whites till foamy on slow speed then add in cream of tartar and continue beating using medium speed till soft peaks from. Increase speed to medium-high then add one-third of the sugar gradually, beat for a further minute, then add one-third more of the sugar gradually. Beat until the egg whites are stiff and fold in the remaining sugar.
Fold in the nuts, chocolate and vanilla into the mixture.
Drop level teaspoonfuls of the mixture onto baking sheets, 4cm apart. Bake for 10 to 12 minutes until the cookies are cracked and firm to touch. Lift the parchment sheets onto wire racks and let the cookies cool completely.