Before beginning please read all my notes below.
Have the dry ingredients weighted and all sifted together in a bowl large enough to hold everything. Sifting makes for a lighter pie crust.
The the butter, egg and milk need to be cold so measure out these second. The butter needs to be cut up into pea size cubes.
Take the cold butter that you have cut up and add it to the bowl.
With the tips of your fingers and avoiding the use of your palms, rub the flour into the butter until it becomes crumbly and should resemble corn flakes
Work quickly to avoid the butter melting. Be light with your finger and toss the flour as you work to keep as much air in the flour as possible.
When the butter is incorporated add the egg and milk and with a fork mix it in.
With your hand reach into the bowl and gently bring all the mixture together.
Tip the contents of the bowl onto your work surface and bring the pastry together. Pushing it into a disk as shown. If it won't hold together add another tablespoon of milk.
You will probably need to use the heal of your hand to give a final push or two to really incorporate the butter. If you find that you have little bits of butter showing that is fine. Don't over work it at this point.
It will be getting warm and a bit sticky by now. So lightly dust it and turn it over and dust the bottom as well.
Shape it into a ball and flatten into a disk, wrap lightly in cling film or place in a plastic bag and put it into the fridge to rest for at least one hour.
Remove and leave on the counter for 10 to 15 minutes to make it a bit easier to roll it out.
Dough can be frozen up to 1 month; thaw in refrigerator overnight before using.
This can of course can be made in a food processor but remember over working the dough will kill it so be gentle when you pulse and do it only enough to bring the mix together.