inspired by https://thewoksoflife.com/hong-kong-egg-tarts/
In a bowl, combine the flour, salt, and 1 tablespoon sugar. Add the butter and break it up roughly with your fingers, making sure to keep visible little chunks of butter in the dough. Add 2 tablespoons of cold water and bring the dough together. Add a tiny bit more water if necessary, but not too much, as this will make your pastry tough. Cover the dough and refrigerate for 20 minutes.
Turn out the dough onto a lightly floured board, knead gently, and form into a neat rectangle. Roll the dough away from you (not back and forth), forming a long rectangular. Fold the top third of the dough down to the center, then the bottom third up and over that. Give the dough a quarter turn (left or right) and roll out again to three times the length. Fold the same way as before, cover, and chill for 30 minutes. At this point, the dough is essentially done.
While the dough is resting, make the filling. Dissolve the 1/2 cup of sugar into the hot water, and allow to cool to room temperature. Thoroughly whisk eggs and milk together and then whisk in the sugar water.
Strain through a very fine mesh strainer. This step is extremely important to getting a smooth, glassy egg tart.
Preheat oven to 400 degrees F and position a rack in the middle of your oven.
Roll out the dough and cut circles to fit in the muffin tin. Then press the dough into the tins.
Fill each tart shell.
Once filled, immediately put into the oven, bake for 15 minutes. Reduce the temperature to 350 degrees F and bake another 10-12 minutes, until filling is just set (if a toothpick can stand up in it, it’s done).