Sift together the flour, baking powder, salt and spices. Beat together the butter and sugar until pale and fluffy. Add the eggs and vanilla essence and mix well.
Add the flour mixture and beat until everything is just blended. Shape the dough into two rolls, about 30 cm long and 4 cm in diameter. Using clingfilm and your hands, square off the sides of the rolls.
Place them on a baking sheet and refrigerate until firm, about 1 hour. Square off the sides once more using the flat side of a ruler and clingfilm and refrigerate for another hour until completely firm. Preheat the oven to 180°C. Cut the rolls into 5 mm thick slices and place the slices on ungreased baking sheets.
Bake for 10-12 minutes or until the edges begin to change colour. Leave to cool on the baking sheets for 3 minutes before turning out onto cooling racks to cool completely.
Icing Beat together the coffee powder, vanilla essence and 20 ml milk until the coffee powder has dissolved. Add the icing sugar and just enough extra milk to make a thick but runny icing. Spoon the icing into a piping bag and pipe thin lines of icing over the cookies.
Spoon the melted chocolate into another piping bag and decorate the cookies. Leave the cookies on the cooling racks to allow the excess icing to run down the sides and harden.