Step 1

Make the puff pastry: Cut the butter into 3/4 cup flour in a medium bowl with a fork, then knead with your hands until the dough comes together. Transfer the “oil dough” to a piece of plastic wrap and pat into a 7 1/2-inch square; wrap in the plastic and refrigerate 20 minutes.

Step 2

Meanwhile, mix the egg, water and remaining 3/4 cup flour in a separate bowl, then knead with your hands until the dough comes together, adding more flour as needed if the dough is too sticky. Transfer the “water dough” to a piece of plastic wrap; wrap in the plastic and refrigerate 20 minutes.

Step 3

Unwrap the “water dough” and roll out into an 11-inch square on a lightly floured surface. Place the “oil dough” square on top and turn it so that it looks like a diamond. Fold the sides of the “water dough” over the “oil dough” to enclose completely.

Step 4

Roll out the folded dough into an 11-inch square and mark it into thirds. Fold in the outer thirds over the center third, like a letter. Roll out the folded dough into a large square again. Repeat twice (folding like a letter, then rolling into a square), refrigerating the dough as needed if it becomes too soft.

Step 5

Mark the square of dough into fourths. Fold the outer fourths into the center, then fold in half like a book and roll out again. Wrap the dough in plastic wrap and refrigerate at least 20 minutes.

Step 6

Butter 12 small (2 1/2- to 2 3/4-inch-diameter) fluted tart pans. Unwrap the dough and roll it out on a lightly floured surface to a 1/4-inch thickness. Cut out circles with a round cutter (about 1/4 inch larger than your tart pans). Refrigerate 20 minutes, then press the dough into the tart pans. Refrigerate until ready to use.

Step 7

Make the egg custard: Heat the sugar and water in a saucepan over medium heat until the sugar dissolves, 3 to 5 minutes. Let cool completely.

Step 8

Whisk the eggs into the cooled sugar syrup, then stir in the evaporated milk, vanilla and salt. Strain through a fine-mesh sieve into a large measuring cup.

Step 9

Preheat the oven to 350˚ F. Arrange the tart pans on a baking sheet. Divide the custard among the pans, filling each about three-quarters full. (Do not overfill or the tarts could overflow; you may not use all of the custard.)

Step 10

Bake until the crusts are golden and the filling puffs slightly, about 45 minutes. Let cool 5 to 10 minutes in the pans, then carefully tap the bottoms to remove the tarts and transfer to a rack to cool completely.