Spread the puff pastry sheets apart and allow to thaw at room temperature for about 20 minutes. In the meantime, drain the apricots well on a sieve, collecting the juice. Finely dice 3/4 of the fruit.
Cut the remaining apricots into slices. Place the puff pastry slices on top of each other and roll out into a rectangle (37x30 cm) on a lightly floured work surface. Place on a baking tray lined with baking paper.
Finely dice the marzipan, mix with the diced apricots, egg white and 100 g icing sugar and spread on the puff pastry. Leave about 2.5 cm free on both long sides. Fold the two short sides and the long sides about 2 cm each.
Spread apricot slices and slivered almonds on the filling. Bake in the preheated oven (electric: 175 °C/ gas: level 2) for 30-35 minutes. Stir the remaining icing sugar in 2-3 tablespoons of apricot juice until smooth.
Take the cake out of the oven and coat the edges with icing. Let them cool down and dry. Makes about 8 pieces.