Put the sultanas in the grappa and leave to soak for approximately 15 mins. Preheat the oven to 190 C (gas mark 5).
In a food processor put the butter and sugar and mix until fluffy. Add the plain flour, the corn flour the baking powder and mix with enough milk to make a dough with a similar consistency to short crust pastry.
Take the mixture out of the food processor and add sultanas to the mixture. Shape the dough in small elongated shapes and cook in the oven until golden (approximately 15-20mins). Once cooked dust with icing sugar.