Melt the chocolate in the bowl of a double boiler (or in a heatproof bowl set over a pan of simmering water). Transfer the melted chocolate to a cool bowl and set aside to cool slightly. If you dip your finger in it after it has cooled a little, the mixture should be slightly warmer than your finger.
In the meantime, combine the sugar and egg whites in another, medium-sized bowl. Mix together until the meringue is glossy and thick and can hold soft peaks. Set aside.
Using an ordinary metal tablespoon, stir the yolks into the cooled, melted chocolate. The mixture will become very thick and practically unmanageable, but keep stirring until the yolks are fully incorporated.
Using the same metal spoon, scoop a spoonful of meringue in the bowl of the chocolate mixture. Stir vigorously to incorporate, then repeat two times. By stirring a few tablespoons of the meringue into the mixture like this, you’re lightning up the chocolate mixture.
Using a rubber spatula, carefully fold one third of the remaining meringue into the chocolate mixture, being careful not to knock the air out of the meringue this time. Repeat with the remaining two thirds of meringue.
Spoon the mousse into pretty glasses, cover with plastic wrap and place in the fridge for at least two hours (or up to 2 days) to set.
Just before serving, whip up the cream with the sugar, spoon or pipe it onto the mousse and top with a fresh raspberry.
Notes
This recipe contains raw eggs. Because of this, it's best not to serve this chocolate mousse to the elderly, children under the age of 5, pregnant women and people with a compromised immune system.
Recipe by The Tough Cookie at https://thetoughcookie.com/2014/04/08/three-ingredient-chocolate-mousse/