Place the puff pastry sheets apart and let them thaw at room temperature for about 20 minutes. Roll out the sheets individually to 11 x 22 cm. Mix egg yolk and 1 teaspoon of cream. Halve 3 rectangles and brush with egg yolk.
Place on a baking tray lined with baking paper and bake in a preheated oven (electric: 200 °C / gas: level 3) for 8-10 minutes. In the meantime, cut a diamond pattern into the remaining rectangles with a large knife.
Cut rectangles in half and place them on a baking tray lined with baking paper. Brush with egg yolk and bake in a preheated oven (electric: 200°C/ gas: level 3) for 8-10 minutes. Let it cool down.
For the filling, whip the remaining cream until stiff. Mix quark, sugar and vanillin - sugar until smooth and fold in the cream. Fill into a piping bag with star-shaped spout. If necessary, press in any squares that are not decorated and spread with approx. 2 tablespoons of plum puree.
Spray curd on top and sprinkle with eggnog. Place decorated squares on top and serve immediately.