Get the ice cream machine running, scoop out the vanilla pod pieces, then slowly pour in the cold custard. Leave it to churn for 10-30 minutes (depending on your machine). When it stops, it is probably too soft to eat, so spoon into a plastic container, cover with cling film, then a lid, and freeze for a minimum of 3 hours. (It will keep in the freezer for 3 months but don’t take it out, then refreeze.) Remove from the freezer 15 minutes before serving.