Wash and drain the plums. Halve the fruits, stone them and cut them into narrow slices. Weigh 1 kg of fruit flesh. Cut open the vanilla pod and scrape out the pulp.
Bring the plums, jam sugar, vanilla pulp and vanilla pod to the boil in a saucepan, stirring constantly. Cook for 3 minutes until bubbly. Remove vanilla pod. Pour slivovitz into the hot jam. Pour immediately into the prepared glasses.
Close well and leave on the lid for 5 minutes.