Whisk together the butter and 75g of sugar until pale in colour. Whisk in the egg yolk and then gently fold in the flour, mixed spice and baking powder.
Add the raisins and cognac to a small saucepan. Bring to the boil,remove from the heat and allow to cool for 5 minutes. This will allow the raisins to plump up and absorb the cognac. Fold the raisins into the biscuit mix.
Tip the dough out on to a lightly floured surface and work gently for 1 minute. Now dust the surface with plenty of flour and roll the dough out so it is roughly half a centimetre thick. Use a fluted cutter to cut the biscuits out.
Preheat the oven to 200'C.
Line a tray with an exopat mat or greaseproof paper. Use a palate knife to transfer the biscuits from the work surface to the baking tray. Lightly prick each one with a fork and put in the fridge for 10 minutes to chill.
Remove the baking trays from the fridge and bake in the oven for 10 minutes. Remove the tray from the oven and lightly brush with the egg white and sprinkle lightly with sugar. Place the tray back in the oven for a further 5 minutes, or until they just begin to turn golden brown. Remove from the oven and transfer to a cooling rack and allow to cool.
«If preparing these in advance, store in an airtight container or wrap several times in cling film.»