Wash, halve and squeeze the oranges.
Put the juice into a bowl (freezer proof) with the Grand Marnier, the seeds from the vanilla pod and the vanilla sugar and freeze overnight.
Put the cream into a pan and bring to the boil, add the coffee beans and sugar and leave to infuse for about 30 minutes.
Strain through a sieve and put into the refrigerator until completely cold (otherwise it will not whip).
Whip the well-chilled cream until stiff and divide between 4 glasses.
Take the granita out of the freezer, scrape off spoonfuls and serve on top of the cream.
Garnish each glass with a piece of orange peel if you wish.