Break the chocolate into small pieces, add the water, and melt in the microwave.

Add the egg yolks one at a time, mixing until the texture is smooth and glossy.

Beat the egg whites with a pinch of salt until stiff peaks form.

Gently fold the beaten egg whites into the chocolate mixture in three additions, using a spatula and lifting from the bottom to the top.

Spoon the mousse into cups or small glasses and chill in the refrigerator for 3 to 4 hours.

Before serving, whip the heavy cream with the powdered sugar, fill a piping bag, and decorate the chocolate mousse with a swirl of whipped cream and a cherry on top.