Cut the vanilla pod open lengthwise and scrape out the seeds. Place both the seeds and the pod together with the whipped cream, sugar, and salt in a saucepan and slowly bring to a boil. When the mixture boils, turn off the heat and keep stirring until all the sugar has dissolved. Cover the pan with a lid and let the cream cool to room temperature.
Remove the vanilla pod from the cream. Beat the butter until fluffy using a hand mixer with whisk attachments. Gradually add the vanilla cream and continue beating. The mixture should ultimately be easy to pipe. If it is too thin, place it in the refrigerator for 10-15 minutes and then continue beating. If the mixture has curdled, briefly heat the bowl in a bain-marie or with a hairdryer and then continue beating.
Line a plate or bowl with baking paper and transfer the filling to a piping bag with a smooth nozzle. Pipe elongated truffles onto the baking paper. Place the plate with the piped truffles in the freezer for at least 1 hour (longer is fine).
Place the cocoa powder in a flat bowl and ensure the melted chocolate is in a bowl that is not too deep. Take the frozen truffles out of the freezer in small batches to prevent them from thawing too quickly. Using a fork, dip each truffle into the melted chocolate, ensuring it is fully coated. Tap off the excess chocolate by gently tapping the fork against the side of the bowl. Drop the truffle into the cocoa powder and cover it on all sides with cocoa. Leave in the cocoa for a few minutes until the chocolate hardens. Do this with all the truffles. You can also roll them in chocolate flakes or shredded coconut.
Set on a parchment-lined plate, and refrigerate them until ready to serve.
Remove the cream truffles from the refrigerator 15-30 minutes before serving.