Drain the plums and collect the juice. Coarsely chop the walnuts. Stir starch with a little water until smooth. Boil up the juice with nuts, cinnamon and 1 tbsp. sugar in a pot. Stir in the starch and let it simmer for about 1 minute while stirring.
Fold in plums. Remove from heat.
Stir pudding powder, 3 tablespoons sugar and 100 ml milk until smooth. Boil up 300 ml milk and cream. Stir in the pudding powder and let it simmer for about 1 minute while stirring. Remove from the stove. Put some compote into 4 glasses (each containing approx. 250 ml).
Pour the pudding into the glasses. Chill for at least 2 hours. Before serving, spread the rest of the compote over the pudding.