Boil up the milk. Remove the pot from the heat, add custard powder and mix well for about 1 minute. Coarsely crumble the Amarettini and stir into the semolina together with the liqueur. Pour the semolina into small, coldly rinsed moulds and place in the fridge for about 1 1/2 hours.
Drain the plums and collect the juice. Stir starch and 4 tablespoons of juice until smooth. Boil up the rest of the juice, cinnamon stick and vanilla sugar. Stir in the mixed starch and bring to the boil once. Add plums and let the compote cool down.
Turn out the pudding and serve with the compote.