Stone, wash and halve the plums. Roughly dice the halves, put everything in a saucepan and let it steep for about 10-15 minutes with the sugar and the vanilla stick. Then bring to the boil and remove the vanilla stick. Let simmer over high heat for about 10 minutes, then remove the pot from the hob. Then add the plum water to the jam. Melt the couverture in a water bath while the jam cools down a little, carefully stir in the melted couverture. Pour everything into prepared jars and close tightly