Mix flour, salt, and baking powder together in a mixing bowl. Add shortening and butter and cut in with a pastry cutter until it resembles coarse crumbs. Stir in the water and egg until well incorporated.
Turn dough out on a floured surface and knead for at least a minute, until it forms a very smooth ball. Use a floured rolling pin to roll out the dough to a circle with 1/4" thickness. It works best to roll a little in all directions, then quickly lift the dough a couple inches off the floured surface, sprinkle some extra flour underneath if needed, and do a quarter turn before laying the dough down again and rolling some more. Repeat this as you roll so you turn it at least 3-4 times - This keeps the bottom of the dough from sticking to your surface. Once you're done rolling, the circle will be larger than you need, but it's always better to have extra crust than not not enough!
Once the dough is the right thickness, gently roll the rolling pin from one end of the dough to the other so the dough is wrapped around the pin and can easily be transferred to a 9" pie dish. Starting at one end of the dish, carefully unroll the dough until it lays over all sides of the dish.
Use kitchen scissors to trim the dough, leaving at least 1/2" over the rim of the pie dish.
Use fingers to crimp the edges of the crust all the way around the pie as pictured above. Make sure the crimped edges extend up past the rim of the dish and lean back just slightly over the rim so it prevents the crust from sagging down too much as it bakes.
Use a fork to prick the crust to allow steam to escape during cooking.
For the egg wash: Use a fork or whisk to beat the egg gently, then use a pastry brush to brush evenly over the crimped edges of the crust (for an extra golden crust, use only the egg yolk). I like to sprinkle with coarse sugar before baking - it's optional but adds a nice touch of sweetness to the finished pie!
Depending on what your pie recipe calls for, can either add the filling and bake or blind bake the crust first by lining it with parchment paper and filling it with dried beans or rice (pictured above) to keep the bottom surface from puffing up while it bakes. To blind bake, place the crust in a 425 degree oven for 10 minutes, or until the edges just begin to brown.