Grease twelve tartlet cups (approx. 3 cm high; 7 cm Ø; alternatively a muffin tray with twelve troughs). Knead 250 g flour and 125 g butter in pieces with your hands until crumbly. Add egg, icing sugar and 1 pinch of salt. Knead first with the dough hooks of the mixer, then with your hands until smooth.
Roll out the dough to a surface lightly dusted with flour to a thickness of approx. 2 mm, cut out circles (approx. 9 cm Ø). Line the moulds with the dough circles and press on the edges. Knead the dough again, roll out and line the remaining baking dishes with the dough. Chill for about 1 hour.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Place the Tartelettes on the oven rack and bake in the oven for 12-15 minutes. Remove from the tartlets and let them cool down.
In the meantime, mix the pudding powder with 25 g sugar and stir it smooth with 100 ml cranberry nectar. Bring 250 ml nectar and 100 g frozen blueberries to the boil. Stir in the pudding powder and simmer everything for about 1 minute while stirring. Stir in the rest of the frozen blueberries.
Pour lukewarm groats into the Tartelettes. Beat the egg white and 1 pinch of salt until stiff. Add 50 g sugar and beat until the sugar is dissolved. Pour the mixture into a piping bag with a small star-shaped spout. Spray the dab onto the Tartelettes. Flare with a kitchen gas burner or just under the preheated oven grill until the tips turn brown.