1. Put the chocolate in a microwave-safe bowl; microwave in 30-second intervals, stirring, until melted, about 2 minutes. Blend the chestnut puree, almond extract, salt and 1 cup confectioners’ sugar in a food processor until smooth. Transfer to a bowl and fold in half of the melted chocolate.
2. Beat the cream and the remaining 2 tablespoons confectioners’ sugar with a mixer until soft peaks form. Reserve 1/2 cup for topping. Fold one-quarter of the remaining whipped cream into the chestnut mixture, then fold in the rest. Chill up to 8 hours.
3. Divide the mousse among dessert glasses. Top with the reserved whipped cream. Remelt the remaining chocolate in the microwave, if necessary, then drizzle on top.