Oil a 9-inch (23-cm) square cake pan, then cover with parchment paper, taking care to let it rise on the sides, making it easier to unmould.
In a double boiler, melt the original milk chocolate drops Chocolats Favoris. Transfer the melted chocolate to a large bowl and let cool for 5 minutes.
Add the marshmallows, graham crackers, and hazelnuts and mix well with a spatula to coat with the chocolate.
Transfer the mixture to the prepared pan and press firmly. Refrigerate for 3 hours. Remove from the pan by pulling the parchment paper. With a sharp knife, cut into bars or squares. Serve immediately, or store in the refrigerator in an airtight dish.