In the bowl of the stand-mixer, whisk gently the 2 yolks with the mascarpone cheese. Then fold the chestnut purée until combined. In another bowl, whisk the 2 whites to medium stiff peaks. Fold delicately to the mascarpone/chestnut mixture. Refrigerate for 2/3 hours.
Cut the meringues (with a knife) into not so small pieces. Put in the glasses where you will serve the dessert. Not too long before serving (otherwise the meringue will absorb the mousse and will "disappear"), pipe or spoon the mousse on the meringue pieces.
Make the whipped cream (with the cream and sugar) using a mixer,(personally I prefer to use an espuma siphon...if you use the siphon, prepare this one night in advance!)
Just before serving, pipe the whipped cream and use one marron glacé as decoration. (if you can't get marrons, or they are too expensive, use a chocolate, or a chocolate truffle