Place the puff pastry slices next to each other and defrost. Drain the cherries in a sieve and collect the juice. Stir 6 tablespoons of cherry juice and pudding powder until smooth. Bring the rest of the juice to the boil, stir in the pudding powder, bring to the boil again while stirring.
Stir in the cherries and fill into a bowl, let it cool down a bit. Roll out puff pastry slices one by one (20 x 18 cm). Spread the stewed cherries on the puff pastry slices, leaving a strip of approx. 2.5 cm wide all around.
Turn the long sides inwards and roll up the discs. Place them on a baking tray lined with baking paper. Prick several times with a fork. Whisk the egg yolk with milk and spread it on the rolls.
Sprinkle each with 1 teaspoon of sugar crystals. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 20 minutes. Remove the cherry strudel. Arrange with 1 scoop of ice cream on plates.
Decorate with 1 cherry and lemon balm.