Boil the water, pour over chopped chocolate, add sweetener (optional).
Whisk with the fork.
Place the bowl over an ice bath and start beating on high with a hand mixer.
First 6-8 minutes mixture will be very thin, but then it will almost instantly turn into a thicker mousse. Stop beating at desired thickness, transfer into serving glasses. Garnish to your liking.
In case you continue, a mass will turn into a very thick (almost solid) paste. You can make truffles out of it with your hands and toss them into cacao powder.
Mousse can be stored in a fridge for up to a week.
