Making the chocolate mousse: Melt the 2 chocolates, which you have broken into pieces, in a large bowl over a bain-marie or in the microwave, making sure the mixture cools slightly.
Whip the cream until soft peaks form, and pour it into the large bowl with the melted chocolate, mixing it into the chocolate mixture.
Now whip the egg whites stiff with the sugar and a pinch of salt and fold them in in 2 additions.
Filling the glasses: Spoon or pipe the mousse into the glasses and smooth the top. Place the glasses in the refrigerator for at least 3 hours to let the mousse set.
Finishing: Dust the top of the mousse with a little cocoa powder. Melt the white chocolate and use a piping bag or paper cone.
Place the chocolate sticks on a tray lined with baking paper and pipe Christmas trees onto the sticks, decorate with sprinkles and let set for half an hour in your refrigerator. Insert the Christmas trees into the glasses just before serving.