Preheat oven to 180°C.

In a mixing bowl, add flour & icing sugar and mix well. Add in cold butter and rub into flour using your fingers. Rub mixture using your hands until it has a rough, crumbly texture (like coarse sand).

Pour mixture onto a baking tray or clean table, make a well in the centre then pour in beaten egg. Gently mix the egg in, then knead mixture using your palm until it forms a smooth dough.

Shape dough into a flattened ball, cover with cling wrap, then keep in refrigerator for 1 hour or longer if needed.

After chilling, remove dough from refrigerator. Roll out the dough into a flat, thin sheet using a rolling pin. Using a round cookie cutter (around the same size as your egg tart mould), cut out 12 circles from the dough sheet.

Place each circle into a tart mould, then using another tart mould, press down onto the dough so as to flatten it and create the zig zag pattern. Use a fork to poke holes at the bottom of the tart shell. Keep the completed ones in the freezer if not baking immediately.

Blind bake (by using pie weights, rice or dried beans) the tart shells for around 15 minutes at 180°C. Remove the pie weights and apply a thin layer of egg wash onto the tart shells, then continue baking the them for another 5-10 minutes until you see the bottom of the tart shell browning. Remove from oven and set aside. Reduce oven temperature to 160°C

Meanwhile, add sugar to hot water, and stir until sugar is completely dissolved.

In a mixing bowl, combine eggs, evaporated milk & vanilla extract. Add mixture into hot water (with dissolved sugar), and use a whisk to gently combine the ingredients so as not to create too much air in the mixture.

Sieve the egg custard mixture two times to ensure the egg custard is completely smooth.

Fill each tart shell with egg custard mixture, up to 90% full. Bake in the oven at 160°C for around 25-30minutes. To check if the egg tarts are ready, insert a toothpick into the centre of the egg tart. If the toothpick can stand upright, the egg tarts are ready. If the toothpick falls, bake the egg tarts a little longer.