Mix the banana nectar and cherry juice well with the preserving sugar in a saucepan. Let it steep for 3 - 4 hours.
Halve the vanilla pod, scrape out the pulp. Add the pod and pulp to the juice in the saucepan. Bring to the boil and let it simmer for about 10 minutes. Make a gel test!
Remove the vanilla pod and pour the jelly into glasses while hot. Close immediately and let cool upside down.