Finely grate the marzipan. Stir the sour cream and marzipan with the whisk of the mixer until smooth. Wash, halve and stone the plums and cut them into very fine slices (approx. 2 mm).
Unroll puff pastry together with baking paper. Prick several times with a fork. Spread evenly with marzipan cream, leaving about 1 cm of edge all around. Cut the dough into about 14 strips (about 3 x 24 cm).
Cover each strip of dough with plum wedges (see fig. 4). Leave an approx. 2 cm wide edge at one end. Roll up tightly (see fig. 5) and place carefully on a baking tray lined with baking paper.
Whisk the egg yolk and 1 tablespoon of water. Carefully brush the edges of the plum roses with the dough. Bake in a hot oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer) for 20-25 minutes.
Remove the roses, dust with icing sugar and let them cool down. Serve with vanilla sauce or ice cream.