With a mixer fitted with a whisk attachment beat the egg yolks with egg whites until volume nearly triples, color is very light and batter drops from beaters in a smooth thick stream.
Lower the speed and sprinkle potato flour and baking powder over egg mixture. Add pisco.
Pour batter into a greased rectangular glass baking dish (13 x 9 x 2 inches).
Bake in preheated oven at 350º F (175° C) for approximately 15 minutes and remove when cake is done. Set aside.
To prepare syrup, combine water (or sweet white wine) with sugar and vanilla.
Bring to a boil over low heat. Add pisco and raisins. Boil 1 or 2 minutes more.
Remove from heat and pour over cake while still hot. Allow to cool.
Decorate with the thinly sliced almonds.
Cut in squares and serve in individual portions.