having problem with chicken pot pie crust
You started out great with cold cold butter and water and then you beat the livin crap out of em for 30 min.

You are making a pie crust.  The thing that makes pie crust flaky is  that the small little pieces of butter, shortening, lard remain intact and then are gently  flattened when you roll out the dough.


  ( good quality lard is best but a combination of butter and shortening will do ). 


The butter, shortening, lard  are not mixed into the flour, they are coated with flour and when you GENTLY roll your dough out you squish them so that you have little layers of lard and flour. When you bake them the lard steams between the layers of flour creating a flaky crust. 

Butter has low melting point so it should be nearly frozen, If you insist on butter cut it into very small pieces and the put it in the freezer. it is best to chill shortening and lard as well.

Cut your butter into your flour/salt mix with a pastry blender cut it together until the lard is in small little pieces about half the size of small peas. Add ICE water ( water with ice cubes in it but you just spoon out the amount you need ) in small increments until it a shaggy dough. (You want it so you can grab a little in your hand a squeeze and it will just hold together.) 

You do not need a mixer but if you use one use it just enough to bring the dough together to the shaggy state. 

Divide the dough into portions appropriate for your pie plate. gently form it into a ball, gently press it flat. Wrap it in plastic and chill it in the fridge before rolling it out. Roll it gently , do not over work it.   

Use the egg wash, cut it with a little water or milk. If you find it is browning to much brush it on part way through the baking time. Do not brush the edges.

Once you do it a few times it will not be a "tonne of work" and you can make enough to keep some in the fridge for a while or freeze some.