2) In a heatproof bowl, cover the sultanas with very warm grappa to 2.5cm above the level of the sultanas. Soak until the sultanas are plumped, about 3 to 5 minutes.
3) In a double boiler, melt the chocolate. Keep warm. Whisk together the flour, cocoa, baking powder and salt. Put aside.
4) With an electric mixer, cream the butter, brown sugar and white sugar until well blended and lighter in colour.
5) Add the eggs, 1 at a time, scraping the sides of the bowl as needed. Blend in the warm melted chocolate, the 2 tbsp warm grappa and the vanilla essence.
6) At low speed, add the dry ingredients in 2 or 3 additions until just combined. Fold in 340g chocolate chunks and raisins. Chill the dough for at least 1 hour.
7) Lightly butter baking trays lined with greaseproof paper. Drop the dough in generous tbsp, about 7cm apart to allow for spreading.
8) Bake for 10 to 12 minutes. The biscuits will look underdone, but will continue to cook and firm as they cool. Stand for 1 to 2 minutes before transferring to cooling racks to cool completely.
9) Well cold, store in a tightly sealed container until required. Enjoy!