Mix the egg and milk together well. Set aside.
Put flour on a cutting board and roll out a pastry pie crust.Use your circle cutter to make as many circles as you can and then put together the rest, roll it out and make more circles as you can. Put a small spoon of ube halaya in each circle. About a tbsp. Test to see if you need to adjust the amount you are putting in the circles. Very gently without pressing, fold the circle together so the edges are about to meet.
Rub eggwash, using your finger tip, all around the edge of a side of the circle.Gently press the circle closed, little by little. Press the middle section a little and then the sides, then press closed everything else.Try not to press any ube halaya filling out and be sure to clean any off if some comes out. Lay the folded, sealed ube handpie down and use a fork to press all through the edge to seal it well.
When all the ube handpies are sealed, space them evenly on the parchment paper/baking sheet and then put them in the FREEZER for 10 minutes.
Preheat oven per the pie crust package directions. Usually 450 F
Take the ube handpies out of the freezer. Slice two tiny slits in each handpie.Brush egg wash on the top of every pie. Bake per pie crust package instructions, but watch the ube handpies that the crust looks slightly golden brown, then take them out the oven. About 10 minutes.
Rest them on an elevated wire rack for 20 minutes. Enjoy!Do not pack together in any sealed container until they are completely cooled or chilled.