In a large bowl, mix together 2 cups of all-purpose flour with ½ cup of chilled unsalted butter until crumbly. Add ¼ cup of sugar, ¼ teaspoon of salt, 1 beaten large egg, and 5 tablespoons of ice water. Knead gently until smooth, then refrigerate for 30 minutes.

In a separate bowl, combine 1 cup of shortening with 1 cup of all-purpose flour and 2 tablespoons of chilled unsalted butter. Mix until smooth, shape into a disc, wrap in plastic, and refrigerate for 30 minutes.

Roll out the water dough into a rectangle, place the oil dough in the center, and fold the water dough over it, encasing it. Roll into a rectangle, fold into thirds, and refrigerate for 30 minutes. Repeat this rolling and folding two more times.

In a mixing bowl, combine ½ cup of hot water with ¾ cup of sugar until dissolved. Beat 3 large eggs and slowly whisk in 1 cup of evaporated milk. Strain the mixture through a fine sieve.

Preheat the oven to 325°F (162°C). Roll the combined dough to 1/8 inch thick, cut out circles for tart shells, and press into molds. Trim excess dough.

Fill each tart shell with custard filling and bake for 25-35 minutes, until set and edges are golden brown.

Allow tarts to cool in the molds for about 10 minutes, then transfer to a wire rack to cool further or serve warm.