In a large bowl, combine flour and salt.

Butter should be soft enough to mold but still hold it's shape. Cut the butter into small cubes and add to the flour. Break the butter up with your fingers, mixing with the flour mixture until it looks like coarse crumbs.

Add cold water and mix the dough with your hands. Dough will be dry. If dough is too dry to stick together, add another 1/2 tsp. of cold water.

Wrap dough tightly in plastic wrap and refrigerate for 20 minutes.

On a lightly floured surface, roll dough into a rectangle about 6" x 15".

Fold the dough into thirds, turn a quarter turn, and roll out again. Fold in thirds once more, cover, and chill for 1 hour in the refrigerator.

While dough is chilling, make the filling. Dissolve sugar into hot water, allow to cool to room temperature.

Mix together evaporated milk, eggs, and vanilla. Once mixed, whisk into sugar water. Strain into a large measuring cup or a pitcher with a spout.

Preheat oven to 375°F. Position rack in the bottom third of the oven.

Roll out dough for the last time, about 1/4" thick. Cut circles about 4" wide, to fit into muffin cups while leaving a lip over the top of the cup. Reroll dough and cut more circles as needed, until you have about 16 rounds.

Fill the tart shells with the filling about 3/4 full.

Immediately place tarts in oven. Once tarts are in the oven, reduce heat to 350°F. Bake for 26-29 minutes until filling is set. You know the filling is set if you can put a toothpick in the filling and it stays standing.

Allow the tarts to cool for 10 minutes before eating.