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The jam is piped between two stacked strips, so it will escape wherever the edges aren't sealed or the filling sits too close to the outer edge. Keep a small border free of jam and press the two layers together along the seam before shaping. Using a thicker jam rather than a runny one also helps it stay put in the oven.

Yes, any thick fruit jam works the same way here - apricot, plum or raspberry all pipe between the layers just like the cherry version. Avoid thin, syrupy preserves or fresh fruit, since the extra liquid will run out and make the pastry soggy underneath. If your jam is loose, stir it smooth and use a little less.

You can cut, stack and shape the strips ahead of time and keep them chilled on the lined baking sheet with the pastry ring in place. Add the egg yolk wash just before baking so it doesn't dry out or soak into the pastry. The powdered sugar should always go on after baking, once the pastry has cooled slightly, or it will simply melt away.

Keep them at room temperature in a loosely covered container rather than an airtight one, since trapped steam turns puff pastry limp. They are at their best on the day they are baked, while the layers are still crisp. To revive them, warm them briefly in the oven and dust with fresh powdered sugar before serving.

Working with pastry that has gotten warm and soft is the biggest one - it won't hold the wave shape and the layers puff unevenly. Letting the egg yolk run down onto the baking sheet is another, as it glues the pastry down and blocks the edges from rising. Finally, opening the oven early or pulling them out before they are properly golden leaves the inner layers doughy.