Make the pastry: in a mixing bowl, cream together the Unsalted Butter and Granulated Sugar until light and fluffy.
Beat in one Egg until incorporated, then fold in the All-Purpose Flour and a pinch of Salt to form a soft, slightly crumbly dough; avoid overmixing.
Gather the dough into a disk, wrap in plastic, and chill in the refrigerator for at least 30 minutes to firm up.
Meanwhile, preheat the oven to 200°C (about 400°F) and prepare a muffin tin or small tart pans by lightly greasing them.
On a lightly floured surface, roll the chilled dough to about 2–3 mm thick, cut rounds slightly larger than your tart wells, and press each round into the pan to form a neat shell; chill the lined tins briefly while you make the custard.
Make a sugar syrup by heating Water with a tablespoon or two of the remaining Granulated Sugar until the sugar dissolves; remove from the heat and let cool to warm.
Whisk together the Evaporated Milk, two beaten eggs, the cooled sugar syrup and a small pinch of Salt until smooth; strain the mixture through a fine sieve to ensure an ultra-smooth custard.
Pour the strained custard into the chilled pastry shells, filling each about three-quarters full so the custard has room to settle and puff slightly.
Bake in the preheated oven for 15–20 minutes, or until the pastry is golden and the custard is just set with a slight wobble in the center; rotate the tin halfway through baking for even color.
Allow the tarts to cool in the pan for a few minutes, then transfer to a rack to cool slightly before serving — best enjoyed warm or at room temperature.
