For the coffee and sponge cake dessert, whip the yolks with the powdered sugar and vanilla sugar in a hot water bath until creamy and thick.
Remove from the steam and continue beating until the cream has cooled. If possible, pre-cool dessert glasses or bowls in the freezer.
Whip the cream until stiff (remove a small amount for decoration) and fold into the yolk mixture with the cognac or rum.
Drizzle the sponge cake with mocha using a brush. Pour cream alternately with drizzled biscotti into dessert glasses or bowls, with the cream as the finishing touch.
Decorate with chocolate chips, cherries (possibly candied cherries) and a dollop of whipped cream. Chill for at least one hour.