Cut the chocolate into large pieces with a knife. Sieve the powdered sugar.
Put the chocolate pieces in a saucepan with the soft butter and powdered sugar. Let the ingredients melt very slowly over a low heat, stirring occasionally. Under no circumstances should the mass get too hot, otherwise the chocolate will become flaky. Then take the saucepan off the stove and let the cream cool down a little.
Separate the eggs. Put the egg whites in the refrigerator. Stir the egg yolks into the chocolate mixture with a whisk. Pour in the whiskey slowly (for men always use the 125 ml whiskey, otherwise use a little less whiskey).
Now whip the egg white and the chilled cream separately from each other until stiff. First carefully (but thoroughly) fold the egg white into the cooled cream, then fold in the cream just as carefully.
Pour the mousse au whiskey into a bowl or in portions into dessert bowls. Chill for about 3 to 4 hours.