Halve, stone and dice the plums. Caramelize the sugar in a pan and add the butter. Put the plums in the pan and add the amaretto. Let the liquid boil off, then put everything in a cool place.
In the meantime, whip the cream until stiff, adding the cream stabilizer after about a minute. Mix the poppy seed cake with the sour cream and then fold in the cream.
Roughly chop the amarettini.
Layer the two masses alternately in a glass, interrupted by a layer of crumbled amarettini.