Place the puff pastry slices next to each other and defrost. Knead flour, sugar, fat, cinnamon and salt with the dough hooks of the hand mixer to form crumbles. Quarter the puff pastry slices. Place on a baking tray lined with baking paper and prick several times with a fork.
Spread each with a tablespoon of plum jam. Sprinkle with crumbles and bake in the preheated oven (electric: 225 ° C/ gas: level 4) for about ten minutes. Let them cool down. Stir icing sugar and lemon juice until smooth, brush cake pieces with it.