Preheat oven to 200°C.

Place butter at room temperature until softened. Cream the butter and sugar with an electric mixer over medium speed until the mixture is smooth, fluffy and light in color.

Add in whisked egg, half at a time, beat over low speed. Add vanilla extract, mix well.

Sift in flour in two batches, scraping down the sides of the bowl between additions with a spatula, and make sure all ingredients combine well. Knead into dough.

Divide the dough into small balls, similar to the size of a gumball. (You can adjust the size depending on the size of your tart tins).

Put the dough ball in the middle of a tart tin, one by one. Lightly press the dough with your thumbs, starting from the bottom then up to the sides.

While pressing the dough, turn the tart tin clockwise/anti-clockwise in order to make an even tart shell. Trim away any excess dough, set aside.

Add sugar into hot water, mix until completely dissolved.Whisk egg with evaporated milk. Pour in sugar water. Mix well.Sift egg mixture to get rid of any foam into a tea pot. Carefully pour egg mixture into each tart shell.

Position rack in lower third of oven. Bake tarts for 10 to 15 minutes until the edges are lightly brown.

Lower the heat to 180C. Keep an eye on them. Once you see the custard being puffed up a bit, pull the oven door open about 2 to 3 inches. Bake for another 10 to 15 minutes until the custard is cooked through. Just insert a toothpick into the custard. If it stands on its own, it?s done :)