In a thick bottomed pan, melt the butter. Add the sugar, stir to combine, then take off the heat and allow to cool slightly.
Then, add the whisked egg, Armagnac and Grand Marnier and pop in the fridge.
Whenever you want to have some of this sauce, lightly whip some cream, add some of the liqueur, butter sugar mix and stir to combine.
The amount of liqueur-mix you add to the cream is entirely up to you, depending on your taste preferences. Just make sure to add a little at a time, until you have the flavour and consistency you want.
The main thing is to enjoy this beautiful festive treat.