Transfer the aquafaba in a bowl and add the cream of tartar (or a little lemon juice if you do not have cream of tartar) along with the sweetener (If using icing sugar, you need to add it later, tablespoon by tablespoon, once the peaks begin to form)

Begin to whisk it at a slow speed for a minute (using hand whisk or stand mixer is recommended) and gradually increase the speed to high. (If using hand whisk, you might need to take two three breaks in between the whisking)

Whisk for 15 – 20 minutes or till the aquafaba forms peaks.

Melt chocolate over bain marie. (I add the chocolate to the bowl once the water begins to boil and the bowl is warm. Then I reduce the heat to low and and allow the chocolate to melt (without stirring). It takes approximately 5 – 7 minutes for this much amount of chocolate. Once the chocolate has nearly melted I switch off the heat and stir it gently so that I get a uniform melted chocolate.)

Remove the bowl from heat and allow the chocolate to cool down.

Once the chocolate has cooled down, take about half a cup (approx. amount) of whipped aquafaba and gently fold it into the melted chocolate. This helps loosen the chocolate and makes it easy to incorporate it into the rest of the whipped aquafaba.

Add the chocolate to rest of whipped aquafaba and gently fold it in, till there everything is well incorporated and there are no white streaks.

Pour the chocolate aquafaba mix into the serving glasses or cups and keep in the fridge for at least four hours or over night. (I believe 100 ml glasses would be ideal to serve this)

Serve chilled. (You can garnish the mousse with some chocolate curls or dust it with cocoa powder but it is optional)

NOTE - You will probably not need sweetener if you are using semi sweet or milk chocolate.