Marsepein-appelflappen

Too much filling is the usual cause, so stick to 1-2 tbsp of apple mixture per rectangle even if it looks sparse. Drain off any juice the apples have released while sitting in the lemon juice and sugar, since liquid loosens the seal. Press the edges down firmly all the way around, and keep the egg wash on top rather than letting it run into the seam, where it can act like a lubricant.

Almond paste works as the closest swap, though it is less sweet than marzipan, so you may want to keep the optional tablespoon of sugar in the apple mixture. If you skip the almond layer entirely, the pockets get noticeably juicier because the marzipan slice sits under the fruit and absorbs some of the liquid. For a nut-free version, leave out both the marzipan and the sliced almonds and add a little extra cinnamon apple instead.

You can shape and seal the pockets, then refrigerate them on the lined tray for a few hours before baking - cold puff pastry actually rises better. Brush on the egg yolk and milk mixture and add the sliced almonds just before they go into the oven so the topping stays crisp. Bake straight from the fridge at 190°C (375°F) and check toward the upper end of the 20-25 minute window.

Keep them uncovered or loosely covered at room temperature for a day or two; an airtight container traps steam and softens the puff pastry. Reheat in the oven at around 190°C (375°F) for a few minutes to bring back the crispness rather than using the microwave. They also freeze well baked - reheat from frozen in the oven and dust with fresh powdered sugar afterwards, since the first dusting dissolves.

Letting the puff pastry get warm and soft while you dice apples and slice marzipan - work quickly, and chill the pastry again if it turns floppy. Cutting the marzipan into thick chunks instead of thin slices also causes trouble, because thick pieces stay dense and stop the pastry underneath from baking through. Finally, dusting with powdered sugar while the pockets are still hot makes it melt away, so let them cool slightly first as the recipe says.