Start off by mixing the shortcrust pastry ingredients into a bowl together with your hands to a firm dough. Wrap it with a cling film or parchment paper and chill for about 30 minutes. In the meantime make the filling.
Using the tip of the knife split the vanilla bean lengthwise and scrape out the vanilla seeds. Mix the scraped out seeds with sugar very well. In a medium pot combine milk (leaving about 5 tablespoons milk behind), vanilla sugar that you've just made, cinnamon stick and empty vanilla bean pod and bring to a boil (at a low heat). Remove from the heat and let infuse for at least 2 hours. In this way the vanilla and cinnamon flavors will be intensified. Then Preheat the oven to 180 ° C (372 °F), with both top and bottom heat.
After chilling the dough, take it out of the fridge. Now you can either either 1) crumble the pastry into a buttered tart pan. Using your hands, press the shortcrust pastry into the pan. Make the pastry a bit high on the sides as well. 2) or you roll out the dough between two parchment papers. Rolling it out this way makes life makes easier. Remove the parchment paper on top, but leave the one at the bottom of the rolled out pastry. Transfer the pastry to a tart tin and make it fit nicely. - (If you want, you can also roll out the pastry dough on a floured work surface with a floured rolling pin. Then transfer it to the tart dish with the help of the rolling pin.)
Now prick the pastry several times with a fork. Use either dried beans, rice, lentils and co. to weigh down the milk tart crust. Simply line the tart dough with parchment paper, add some weight and blind bake for 35 minutes. Feel free to remove the weight 5 minutes before the end of baking time, so that the crust will become nicely golden brown. Remove the tart crust from the oven, followed by the weight and let cool completely before filling. This takes about 2 hours.
Now it's time to go back to making the milk tart filling. After 2 hours, heat the cinnamon-vanilla-milk mixture on low heat and remove the vanilla pod and cinnamon stick. Whisk together cornstarch, plain flour, an egg and leftover milk and add mixture to the pot. Keep stirring constantly until the custard thickens.
Stir in the butter and immediately pour the filling into blind baked tart crust. Let cool to room temperature for an an hour. Then place it in the refrigerator until the filling has completely set. Sprinkle with cinnamon just before serving and enjoy.