Place the chopped chocolate and heavy cream in a heatproof bowl set over a saucepan of simmering water (double boiler). Stir until chocolate is melted and smooth. Remove from heat and let it cool slightly.

Carefully separate the egg yolks from the egg whites. Place yolks in one bowl and whites in another, ensuring no yolk gets into the whites.

In the bowl with egg yolks, add granulated sugar. Whisk vigorously until the mixture becomes pale yellow and slightly thickened (about 2-3 minutes).

Slowly pour the melted chocolate into the egg yolk mixture, whisking constantly until well combined. Ensure chocolate isn't too hot.

In the bowl with egg whites, add salt. Using an electric mixer, beat egg whites until stiff peaks form. Be careful not to overwhip.

Gently fold one-third of the whipped egg whites into the chocolate mixture to lighten it. Then, gently fold in the remaining egg whites in two additions, being careful not to deflate them.

Spoon or pipe the chocolate mousse into individual serving cups or glasses.

Cover cups with plastic wrap and refrigerate for at least 2 hours, or preferably overnight, to allow the mousse to set properly.