Let the strudel dough rest for about 10 minutes at room temperature. Peel and quarter apples and cut out the core. Apples
Melt the butter. Place a damp tea towel on the work surface and a dry one on top. Take the strudel leaves out of the package and unfold them. Place 1 sheet on the cloths, spread a thin layer of butter on top.
Place the remaining 3 leaves on top, each rotated by 90 degrees, brushing each leaf thinly with butter.
Sprinkle strudel dough evenly with ground almonds. Leave a rim of approx. 12 cm on the upper side and a rim of approx. 3 cm on the other sides. Spread apples evenly on the almonds.
Finely grate the marzipan. Sprinkle with almond slivers.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Line baking tray with baking paper. Roll up the dough firmly from the bottom to the side with the wide edge using the tea towels.
Place on the sheet with the cut edge facing down. Whisk the egg yolk and 2 tbsp. water. Spread a thin layer of the whisk.
Bake in the hot oven on the lower shelf for 25-30 minutes. If necessary, cover carefully with foil 10 minutes before the end of the baking time. Remove and let cool on a cake rack. Dust with icing sugar.
Goes well with vanilla sauce.