Mix the flour, vanilla, salt and yeast in a bowl. Add the milk, quark and butter, mix, knead for approx. 10 mins. to form a soft, smooth dough. Cover and leave to rise at room temperature for approx. 2 hrs. until doubled in size.
Divide the dough into 8 portions, shape into balls. Flatten the balls, stretch out into rounds (approx. 12 cm in diameter), creating a 1 cm high rim around the edge, place on two baking trays lined with baking paper. Brush the edges of the dough with egg, set aside the remainder of the egg.
Mix the quark with the reserved egg, cornflour, almond mixture and vanilla. Spread the custard in the middle of the pastries, top with the plums.
Approx. 30 mins. in an oven preheated to 200°C (convection). Remove from the oven, leave to cool completely on a rack. Dust the plum pastries with icing sugar.