Wash the berries, drain them and remove the stems (frozen fruits can of course also be used).
Put the fruits in a saucepan. Add the inside of the vanilla pod (if you like, you can add more vanilla) and mash the whole thing with a potato masher. Add the preserving sugar and bring to the boil while stirring over high heat, simmer for at least 3 minutes, stirring constantly. Then remove from the hotplate.
Immediately fill the prepared glasses to the brim. Close with twist-off lids, turn over and leave on the lid for about 5 minutes.