Preheat oven to 170° (circulating air). Clean the rhubarb and cut it into pieces about 1 cm wide.
Cream butter, 125 g sugar, vanilla sugar, cinnamon and a pinch of salt with a hand mixer. Stir in one whole egg and two egg yolks (save the egg white for the meringue!) one after the other.
Briefly stir in flour, starch and baking powder. Add the rhubarb.
Fill dough into paper cups or a muffin tray and bake on the second rack from the bottom for 20 minutes.
In the meantime, beat the two egg whites with a pinch of salt until stiff, add 100 g sugar while stirring and continue stirring until the sugar has dissolved.
Spray the beaten egg white decoratively on the tartlets and put them in the oven for another 10 minutes.
Let it cool down - or best still enjoy it warm!
(Gives about 16 pieces).