In a bowl, add both icing sugar and vanilin sugar to the butter and whisk the mixture with an electric mixer on medium speed until it is fluffy and soft. You can whisk the mixture with your hand too.
Add one egg to the mixture and mix it again.
Now add the all purpose flour to the bowl and combine all ingredients.
Once you are done, spread a generous amount of flour onto your working top and knead the dough. If it is sticky, just spread a little more flour on the table and onto your hands. Knead the dough until it is smooth and non-sticky. After which, wrap a cling wrap over the dough and let it rest in the fridge for at least 15 mins. The longer, the better. While the dough is resting, we could move on to making the custard filling.
Over a medium heat, warm up milk in a small pot and add in the sugar to dissolve it. Turn off the heat. Let the milk-sugar mixture cool down.
While the milk-sugar mixture is cooling, we could work on the dough again. Firstly, thinly coat your muffin tray (or tart forms) with some butter and spread a little flour over the each mould. This is to ensure that the tart shells do not stick onto the tray after baking.
Once the dough is well rested, take it out of the fridge and spread some flour onto the working area, your hands and a rolling pin. Cut the dough roughly into 3 pieces and preheat the oven to 180°C.
Let us work on the first piece of dough and cover the rest with cling wrap, so that they do not dry out.
Roll out the dough to a thickness of approx. 3-5 mm. The tart shells should not be too thin, as they would break when you try to get them out of the muffin tray. Cut them with a cookie cutter or in my case, with a cup. Place them over the muffin tray and use your fingers to press them down gently into the mould and gently use the fork to prick a few holes on the crust.
Once the milk sugar mixture (Step 5) is cooled down, add the whisked eggs, vanilla extract, a pinch of salt and the cream into the mixture. Sift the mixture to get rid of any clumps.
Pour the mixture (Step 10) into each crust (Step 9). The filling should fill up roughly 80% of the crust.
Once you are done, bake your egg tarts in the preheated oven for 20-25mins (depending on your oven).
Once it is done baking, take the tray out, poke one tart with a toothpick to see if the filling is cooked (if the toothpick is clear) and let them cool for about 10 mins before trying to get them out of the tray. You can serve your egg tarts either warm (which is extremely delicious) or at room temperature.