Put your vanilla sugar in an airtight jar and keep, if possible, 3 weeks before using, so that the vanilla aromas mix well with the sugar.
During these three weeks, stir it with a fork once a week, so that it does not form lumps.
Remarks
You can make multiples of the proportions indicated, but it is important to respect 100 g sugar per vanilla pod.
Don't believe those "recipes" who tell you that putting a vanilla pod in a jar of sugar will give you vanilla sugar, it's a lie because the vanilla pod is impervious.