This step is optional. I use leftover ganache that I've molded beforehand, to avoid wastage.
Heat the cream (1) with the half vanilla pod, split and scraped, and leave to infuse for 30 minutes, covered.
Meanwhile, melt the chocolate in 30-second bursts in the microwave.
Remove the vanilla pod and pour the hot cream over the chocolate in 3 batches. Emulsify with a Maryse.
Pour in the cold cream (2), mix, seal and chill for at least 4 hours.
After resting, whip up the ganache and fill the quenelle molds. Place in the freezer until completely hardened.