Add sugar to the Thermomix bowl. Mill for 10 seconds / speed 9. set aside.
Insert the butterfly attachment. Add the cream to the bowl and whip for around 1 - 1:30 minutes / speed 3. Watch it carefully from 30 seconds onwards and keep an eye out for the texture changing. You want it to be thick and fluffy. Set aside.
Break the chocolate into pieces and add to the bowl with the butter. Melt for 4 minutes / 50 degrees / speed 2. Check that it is fully melted, if not repeat for a further 1-2 minutes.
Add the egg yolks, whipped cream and Cointreau/Grand Marnier (if using). Mix for 15 seconds / speed 4. Set the mixture aside in a large bowl.
Now clean and thoroughly dry the bowl and insert the butterfly attachment.
Add the egg whites and whisk for 90 seconds / speed 3.5.
Add the sugar and continue to whisk for a further 1 minute / speed 3.5.
Use a spatula or spoon to fold the egg whites into the chocolate mixture. You want it to be well mixed but don't over mix it. You want to keep it light and airy.
Divide the mixture into serving bowls and chill in the fridge for a minimum of 2 hours before serving.
Top with whipped cream and grated chocolate to serve.