Melt most of the dark chocolate in a bowl over hot water, reserving a small portion to grate for topping.
Pour the white beans into a sieve, catching the liquid (aquafaba) in a bowl below.
Use an electric whisk to whip the aquafaba for a few minutes while the chocolate melts.
Once melted, add the drained beans to the chocolate and blend together in a jug blender or food processor, scraping down the sides as needed.
Continue to whisk the aquafaba until stiff peaks form, about 8-10 minutes. Stiff peaks occur when you can turn the bowl upside down without the mixture moving. There’s no need to worry about over-whisking aquafaba.
Gently fold the chocolate and bean mixture into the whipped aquafaba until well combined.
Pour the mousse into 4 serving dishes and chill for an hour.
Before serving, sprinkle the mousse with the grated chocolate.
Store the protein mousse in the fridge and enjoy within 3 days.