Preheat oven to 180C and position rack in lower third of oven.
Completely dissolve the sugar in the hot water and set aside to cool.
Roll out the pastry dough to 12 x 12 inches or 14 x 14 inches and cut out 9-12 circles using a 4 inch cookie cutter. Fit the pastry circles into the foil tart tins and place on baking sheet.
Whisk the eggs, egg yolk, evaporated milk, vanilla, and sugar water together. Stir in the sugar solution. Strain the egg mixture into a large measuring cup through a sieve. Carefully pour into tart shells, filling to just below the rim.
Bake for 10-15 minutes until the edges are lightly brown. As soon as the custard starts to puff, open the oven door 2-3 inches to prevent the filling from puffing up too much and collapsing when cooled.
Once the edges start to brown, reduce the heat, and bake for another 10-15 minutes or until the custard is done. You can test the filling by inserting a toothpick into the custard, if it can stand on its own, it’s done.