Mantelileivokset

Yes - the recipe works with any laminated pastry dough, so frozen puff pastry is fine as long as you thaw it fully and unroll or roll it into a rectangle first. Keep the dough cold when you spread the almond cream, otherwise the butter in the layers softens and the roll gets sticky and hard to slice. If your sheet is thinner or larger than a standard one, spread the cream a bit thinner rather than piling it on.

Ground almonds with skins on (or almond flour) work in the same 100 g quantity; the filling will just look a little speckled rather than pale. If you want to skip the egg white, add another 1-2 tbsp of cream or milk instead until the almond cream is smooth and spreadable - its job here is binding, not leavening. For the egg wash you can brush with just milk or cream, though the pastries will bake up less deeply golden.

Usually the roll was rolled too loosely, or the cream was spread too thickly right to the edges so it had nowhere to go but out. Roll tightly from the long side and chill the roll for the full 10-15 minutes before cutting - cold cream stays put much better. Also press the chopstick straight down once into the center rather than wiggling it around, since that widens the hole and opens a channel for the filling.

Yes - you can make the almond cream a day ahead and keep it covered in the fridge, then let it sit at room temperature briefly so it's spreadable again. The rolled log can also be assembled ahead and chilled longer than the 10-15 minutes; a well-chilled roll actually slices more cleanly into the 4.5 cm pieces. Shape, brush with the egg-yolk-and-milk wash, and add the sliced almonds just before they go into the 180 °C oven.

Keep them at room temperature in a loosely covered container or paper bag rather than an airtight one, so the laminated pastry doesn't go soft from trapped steam. They're at their flakiest on the day they're baked. To revive them, warm them for a few minutes in the oven at baking temperature, let them cool, and dust with powdered sugar afterwards - sugar dusted before reheating just melts away.