Wash the plums, halve them and remove the stone. Take the puff pastry out of the fridge 5-10 minutes before processing. In the meantime, stir the quark, 1 egg yolk, sugar and sauce powder with the whisk of the hand mixer until smooth.
Whisk 1 egg yolk and milk. Remove the puff pastry from the packaging and unroll it on the baking paper. Halve the puff pastry sheet 1x lengthwise and then quarter it to make 8 pieces. Pour curd mixture evenly into the middle of the pieces.
Put two plums in each. Fold two opposite tips of each piece of dough towards the middle and press lightly. Carefully place the pieces of dough (possibly with the help of a pallet) on a baking tray lined with baking paper.
Brush with whisked egg yolk and press a nut onto each seam. Sprinkle with decorating sugar and bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-25 minutes.
Remove from the oven, place on a cake rack and allow to cool.