Cut open the vanilla pod and scrape out the seeds. Put both the marrow and the stick together with the cream, sugar and salt in a saucepan and slowly bring to the boil. When the mixture boils, remove the pan from the heat and keep stirring until all the sugar has dissolved. Cover the pan with a lid and let it cool to room temperature.
Remove the vanilla pod from the cream. Beat the butter for a few minutes until fluffy. Gradually add the vanilla cream and continue beating. The mixture should eventually be easy to spray. If it is too thin, place it in the fridge for 10-15 minutes and then continue whisking. If the mixture has split, heat the bowl briefly in a bain-marie and then continue to whisk.
Line a plate or dish with baking paper and place the filling in a piping bag with a smooth nozzle of 1 – 1 centimeters. Pipe elongated truffles onto the baking paper. Place the plate with sprayed truffles in the freezer for at least 1 hour (longer is allowed).