Roughly chop the dark chocolate and add it to a double boiler (see notes) along with the plant-based milk.
Allow the chocolate to slowly melt into the plant-based milk for about a minute and then gently stir with a whisk until the chocolate is completely melted and smooth. Set aside to cool.
Before beating the aquafaba, make sure your mixing bowl and whisk is completely grease free by rubbing it down with a cloth or kitchen towel. Any oil or grease will cause the aquafaba to fall in on itself and not rise.
Add the aquafaba to your mixing bowl and beat on high for roughly 10 - 15 minutes until stiff white peaks form.
The chocolate should have cooled down to room temperature by now and you can add it to the beaten aquafaba. Fold it in gently until the chocolate has been completly worked through.
Pour the mousse mixture into your serving dishes, cover and place in the refrigerator for a minimum of 4 hours (we find that cooling them overnight works best).
Once your vegan chocolate mousse has completely set, serve and enjoy!