Let the puff pastry sheets thaw. If you have fresh puff pastry, don't.

Meanwhile, wash the plums, halve them, and remove the pits. Grease the tartlet tins with butter. Unroll the puff pastry. Cut out 10 circles (10 cm in diameter). Place the icing sugar in a sieve and sprinkle it evenly over the tins. Place the puff pastry in the tins and press it down.

Preheat oven to 200 degrees (180 degrees fan-assisted).

For the almond cream: Grate the marzipan and butter using a coarse grater. Bring the milk to a boil. Combine the egg yolks, cornstarch, and sugar. As soon as the milk is almost boiling, add a splash to the egg yolk-cornstarch-sugar mixture to temper it. After adding three splashes to temper the mixture, pour the entire mixture back into the remaining milk and bring everything to a boil. Cook for 1 minute, until thickened.

Add grated marzipan and grated butter to the hot mixture and work it in until completely dissolved. The mixture is easiest to work with while still very warm. Spread the marzipan cream over the pastry base and arrange the plums on top. Bake in the oven for 20 minutes. Let the plum and marzipan cream tartlets cool slightly, dust with powdered sugar, and then serve.