Put Flour, salt, sugar and butter into food processor. Pulse until the butter is broken up pieces the size of peas. Add the cold water and pulse till it forms a dough. Cover and let rest in the refrigerator for 20 minutes.
Once chilled, turn the dough out onto a floured surface, knead a bit, then roll out into a rectangle thats about 8X20 inches. Fold the top half of the dough to the center then fold the bottom half so that both ends are meeting in the middle, Fold the dough over again like a book. It will look like a long rectangle. Turn it 90 degrees, then roll the dough out again. This time roll it out to 3x the length. Make the same folds are before, wrap and chill in the refrigerator for 30 minutes.
To make the custard, start by making the simple syrup, dissolve the sugar into the hot water and let it cool to room temperature. Whisk the eggs, evaporated milk and vanilla together. Slowly whisk in the cooled simple syrup and Black sesame paste. You'll see flecks of sesame in your custard
Pre Heat the oven to 400F. Once the dough has chilled the second time, roll it out on a floured board to about 1/4 inch thick. Too thin and it'll break apart when you try to take them out after they're baked. Cut 4 inch rounds. Place into the mini muffin tin. Push down to create the well and push the dough up the sides of the tin to make sure the crust doesn't shrink while baking. Pour the custard into each well filling it about half way. Too much and they'll overflow in the oven, making it hard to pop out of the tins when they're done.
Carefully place the tins in the oven and bake for 9 minutes. Then turn down the oven to 350 and bake for another 10-13 minutes till the custard is set. Let them cool in the tins for about 5-10 minutes to make them easier to pop out. Enjoy warm!