Simple version of Hong Kong Style Egg Tart.
Preheat oven at 360 F/180°C.
Combine granulated sugar and hot water until the sugar dissolves. Set aside to cool.
Cut puff pastry sheet into 9 squares (or you can cut the squares into circles using cookies cutter to fit the tart molds). Press down the dough onto the lightly-greased tart molds and poke some holes on the bottom.
Beat eggs, milk, vanilla extract, and salt until smooth. Combine with sugar mixture. Strain the mixture twice to achieve smooth egg mixture.
Pour the egg mixture into the tart molds
Bake for 30 minutes until golden brown. Let it cool on the tart molds for 5 minutes. Remove the molds and transfer to wire rack. Serve warm.