Place the finely chopped chocolate, coconut cream and vanilla extract in a heatproof bowl set over a pan of gently simmering water. Don't let the base of the bowl touch the water.
Stir until almost all of the chocolate has melted then remove the bowl from the heat and continue to stir until melted and smooth. The ganache should be smooth and glossy, see tips in the post above if it goes oily or grainy.
Set the ganache aside to cool to room temperature.
While the gananche is cooling, place the aquafaba and cream of tartar in the bowl of a stand mixer fitted with a balloon whisk; or use a hand mixer with the double beater attachments.
Whisk the aquafaba on a high speed until it is frothy, add a spoonful of the sugar and whisk until well combined; repeat until you have added all of the sugar. Continue to whisk the aquafaba until it forms stiff peaks. This can take 10-15 minutes.
Make sure that the chocolate mixture has cooled to room temperature then add ¼ of the whipped aquafaba to the chocolate and stir gently with a spatula until almost combined.
Add the rest of the aquafaba in three more batches, folding it in very gently until it is uniformly combined. You don't want there to be any more streaks of chocolate or aquafaba, but don't keep mixing for too long, you don't want to deflate the mousse. (It will lose a bit of volume however and become slightly more runny - don't worry, this is normal).
Divide the mousse evenly between 4-6 glasses and place it in the fridge for at least 4 hours until set. (I leave mine overnight).