Halve the vanilla pod lengthwise and scrape out the pulp with the back of a knife. Bring milk, vanilla pulp and pod to the boil in a pot. Mix 3 egg yolks and sugar until light creamy. Stir the starch into the sugar-egg mixture.
Add a part of the vanilla milk while stirring, then pour back to the remaining milk.
Bring the cream slowly to the boil while stirring. Pour cream into a bowl and cover the surface directly with foil. Chill the cream for about 45 minutes. Remove puff pastry from the fridge 5-10 minutes before use.
Roll out the puff pastry. Cut out 12 circles (approx. 9 cm Ø) from the dough. Cut a small circle (approx. 6 cm Ø) out of 6 circles in the middle. Lay the dough on top of each other, roll out again and cut out about 4 more circles.
Cut a hole in the middle of 2 circles again.
Whisk 1 egg yolk and 1 tablespoon of water. Brush circles with some egg yolk, then place a dough ring on each circle. Brush the edges of the dough with egg yolk again and place on a baking tray lined with baking paper.
Bake the tartlets in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for 15-20 minutes. Take out.
Stir the custard until smooth and fill into a piping bag with a medium perforated spout. Spray cream onto the middle of the tartlets and dust with icing sugar. Caramelise the tartlets slightly in the oven at the same temperature.
Let it cool down and serve.