Let's prepare the ingredients. Add the salt to a small bowl of water and stir to dissolve. Add the beaten egg and mix. Refrigerate the egg mixture, flour that has been sifted, and unsalted butter until ice-cold.
Let's make the tart dough. Place the chilled cake flour into the bowl of a food processor. Add the butter diced into 1cm (0.4") cubes. Lightly even out the ingredients.
Cover and blend the mixture for about 15 to 20 seconds. The butter pieces should be about half the size of a rice grain.
Add the egg mixture. Continue to blend the mixture for about 15 to 20 more seconds. When the mixture turns yellow and forms moist large clumps, stop the processor.
Place the mixture onto a work surface covered with a sheet of plastic wrap. Pull the edges of the plastic wrap to the center and gather the clumps into a ball. Then, flatten the dough.
Dust a scraper with bread flour and divide the dough into 4 pieces. Stack the pieces on top of each other, sprinkle over flour and flatten the dough with your palms.
Adjust the edges, shaping the dough into a disk. Wrap the dough with the plastic wrap and let it sit in the fridge for 1 to 2 hours or overnight.
Transfer the dough to a work surface dusted with bread flour. Lightly flour the dough and a rolling pin. Press the rolling pin into the middle of the disk. Rotate and press it again. Repeat the process in all directions.
Roll out the dough from the middle outwards. Then, roll it out from the middle towards you. Rotate the dough 90 degrees and repeat the rolling process. If it sticks, dust the dough and rolling pin and quickly roll it out. The circle should be about 27cm (10.6") in diameter and 3mm (0.1") thick.
Flour the top of the dough again. Using a fork, pierce the dough in numerous places.
Remove the 21cm (8.3") tart pan from the freezer. Loosely roll the dough around the rolling pin. And then unroll it onto the chilled tart pan with a removable bottom.
Dust your fingers with flour and press the dough up the sides of the pan. Be sure to push the dough into the corners to remove any gaps.
Cover the rim of the pan with the dough. Then, run the rolling pin along the top of the pan. Trim the edges of the dough to fit the tart pan. Lightly press the top and sides again to firmly attach them together.
Prick the dough all over with a fork again. This will help the air to go through the dough and keep the bottom from rising. Let the tart pan rest in the fridge for 30 minutes or chill it in the freezer for about 3 minutes.
Preheat the oven to 190 °C (374 °F) and place the tart pan into it. Bake the tart at 190 °C (374 °F) for a total of about 20 minutes. To help brown the tart evenly, put on kitchen gloves and rotate the pan after about 15 minutes. Then, bake for 4 to 5 more minutes.
You will bake the crust with filling later so remove it when the whole surface is slightly browned. Place the pan onto a cooling rack. Let it sit to cool and then remove the tart crust from the pan.
This dough doesn't contain any sugar so in addition to making dessert tart, you can also make non-sweet pastry dishes like quiche with it.