Preheat oven to 180 degrees C. Cut a round of baking paper the size of the bottom of the cake tin. Butter the sides of the tin and one side of the paper. Lay the paper butter side up in the tin and dust thoroughly with flour.
In a small bowl combine sultanas and scotch whiskey then set aside.
Place chocolate in the top of a double boiler with 3 tablespoons of water. Stir until melted and smooth. Remove from heat and stir in the butter in small pieces.
In a large bowl beat the egg yolks with the sugar until the mixture is a pale creamy yellow. Combine with the chocolate mixture.
In a small bowl combine the flour and the ground almonds then add to the batter. Stir in the sultanas and whiskey.
In a clean large bowl whisk the egg whites with a pinch of salt until they are stiff but not dry. Stir a third of the egg whites into the chocolate mixture to lighten it then fold all back into the remaining egg whites. Pour the cake mixture into the prepared cake tin.
Bake at 180 degrees C for 20 minutes. The outside should be firm but the centre should remain moist. Let the cake sit for 10 minutes in the tin then unmold it on a cake rack and let it cool for a few hours or overnight. Peel off the paper before icing it.
Icing: Melt chocolate in the top of a double boiler. Stir in the icing sugar and then the butter a little at a time. Blend well and spread immediately on the cake. Allow icing to set for about half an hour before serving the cake.