In a saucepan placed in a bain-marie, melt 8 oz dark chocolate with the butter and Grappa. Whip the eggs and sugar in a bowl until it forms a foamy mixture. Then add the lukewarm chocolate mixture and mix until everything blends well.
Folding in from top to bottom, add the sifted flour with the yeast and salt. Once a homogeneous mixture is obtained, leave to cool in the fridge for 2 hours.
When chilled, add the rest of the dark chocolate chips and shape large walnut-size balls with your hands, then roll them in the icing sugar. Cover a tray with baking paper and arrange the chocolate cookies in a well-spaced manner.
Bake the chocolate and Grappa cookies in the oven at 356° F for about 20 minutes. Allow the cookies to cool before removing from the tray and serving.