Melt the chocolate in a heatproof bowl over a pan of gently simmering water, then remove to cool for 10 minutes. Meanwhile, simmer the cherries and their syrup in a non-stick frying pan on a medium heat until thick, then remove.
Whip the cream to very soft peaks. Separate the eggs, add the yolks to the cream with the sugar, and whisk to combine. Add a pinch of sea salt to the whites and, with a clean whisk, beat until super-stiff. Fold the cooled chocolate into the cream, then very gently fold that through the egg whites with a spatula.
Divvy up the mousse between six glasses or bowls, interspersing the cherries and syrup throughout, and finishing with a few nice cherries on top.