Sift the flour in a bowl and place the chilled and cubed (small ones) butter in it.
With your fingers, rub the butter with the flour till the butter mixes with all the flour and resembles a grainy crumbly texture. Add the castor sugar and mix thoroughly.
Make a well in the centre of the flour mix. Pour the juice of one orange and the entire grated orange zest into the well. If the orange is very small, you may need a little bit of extra orange juice. It is completely on judgement. There should be just about enough orange juice to bring this dough together. It should not be too moist also.
Now flatten the dough, cut in into 2 batches and cover it completely in cling film and place in the refrigerator for about 20 minutes. I like to keep the pastry in batches, since it is easier to roll out, when in small batches.
In the meanwhile pre heat the oven at 180 degree Celsius.
After 20 minutes, take the dough out and place it on a cling film on both sides. I find it easier to roll on pastry using the cling film, since it reduces the chances of the pastry breaking or sticking to the rolling pin. You can use butter paper for the same too or simply dust the surface with extra flour for rolling.
Using a rolling pin, start rolling out the pastry to about 2- 3 mm thickness. Remove the cling film from top. Take a round cookie cutter little bigger in size than the size of your pie shells. Cut out round shapes and place them in your pie shells.
With your fingers, line the entire pie tray with the pastry. Once it is complete, scoop out mince meat into the shells till the top.
Roll out rest of the pastry and cut out star shapes and place them on top of the mince meat.
Brush the top of the stars with some egg wash. If you do not want to use eggs, then just brush with some milk.
Bake the pies in a pre heated oven at 180 degrees for about 20 minutes or till its golden.
After 20 minutes, take the tray out. Let it cool down a bit. Then using a knife, gently lift the side of each pie and tip it out of the tray.
When the pies are completely cool, sprinkle some icing sugar if you want to. The mince pies are generally very sweet and do not require extra icing sugar.
You can store them in air tight containers. Good luck trying to keep them for a longer period of time. They are very addictive.