Peel the skin off the peaches. But that only works if the peaches are really ripe. Otherwise, put in boiling water for 10-15 seconds before halving, then the skin can be peeled off. Then halve and cut into small pieces.
Add the syrup, vanilla sugar (not vanilla sugar), lemon juice and kirsch, mix well and let steep for 2-3 hours. Mix it up again and again during this time.