Chop the chocolate into small, even pieces and set aside.
Gently warm the heavy cream over low heat until steaming, not boiling.
Add the chopped chocolate to the warm cream and stir until smooth and glossy. Set aside to cool slightly.
Separate the egg yolks and whites into two clean bowls.
Whisk the egg yolks with granulated sugar until pale and smooth.
Whip the egg whites to soft or stiff peaks, depending on desired texture.
Stir a small scoop of egg whites into the chocolate mixture to lighten it.
Gently fold in the remaining egg whites using wide, careful strokes.
Spoon the mousse into individual cups or ramekins.
Cover and refrigerate until fully set, at least 2 hours or up to 2 days.