Wash and stone the plums and cut them into slices. Melt butter. Caramelise 3 tbsp. sugar in it while stirring. Stir in juice, bring to the boil and simmer for 2-3 minutes. Cut the vanilla pod lengthwise and scrape out the pulp.
Add the plums, vanilla pulp and vanilla pod to the juice and bring to the boil. Cover and simmer for about 3 minutes. Stir starch and 4 tbsp. water until smooth. Bind plums with it. Season soup with 1-2 tbsp. sugar and let it cool down.
Then cover and leave to cool for at least 2 hours.
Beat the egg white and lemon juice until stiff, adding 2 tablespoons of sugar. Cut off small dumplings with two teaspoons. Put them into boiling water in a pot. Cover and let simmer for 4-5 minutes.
Remove the vanilla pod from the soup. Serve cold dish with snow dumplings.