My Mom was an excellent pie baker and this was found in her recipes by my niece, Stephanie. I did not recall seeing her put an egg in her crust (she had more than one recipe, I think) so I investigated to see what the difference is.
This is what Aimee the editor at simplebites.net says about butter and egg in pie crust: They add richer tastes, color beautifully, taste buttery, and crisp just right.
The baking powder helps make a lighter crust. It turns out that adding egg is the French style of making pie crust.
1Mix dry ingredients, cut in the cold butter with a pastry cutter -- or a fork -- till crumbly
2In a separate cup beat the egg with a fork and add the vinegar and ice water. Blend well.
3Add the wet to the dry ingredients, do not overwork, you are not making bread. Pie dough must be handled as little as possible so you do not activate the gluten which will make it tough. Just mix it enough that it holds together and resembles slightly crumbly pie dough. It will come together better after the cooling period.
4Separate the ball of dough into 2 equal pieces, form them into flattened balls, and wrap in plastic wrap, and put in the fridge for 20-30 minutes (up to an hour). The cold rest will help to make the crust flaky. It will also make it easier to roll out.
5Remove from fridge, roll out about 3-4 inches larger than pie plate on floured surface, fold in quarters and place the point in the middle of a glass pie plate. Then unfold and gently press and fit it to the pan. (Glass cooks more evenly.) Fill 2 pies, or fill 1 pie and cover with other crust.
6If making open pie crusts, do not trim the edges completely off. Tuck about an inch of excess dough under evenly with the edge to build up the edge so you have enough crust to pinch them evenly without breaking. If making a top crust, then trimming the edges a half inch from the edge of the pan will allow enough to tuck and build up the edges for crimping (because there are two layers of dough).
7Cut three or four 1" slits in the top crust for air and bubble vents.
8If making a shell to bake now and fill later, then use a fork to put many holes in the crust to keep it from bubbling up.
9FOR BAKED PIE SHELL: Bake 350 F for 10-15 minutes or until golden brown
10FOR FILLED PIE: Bake 400 F for 15 minutes
Then bake 350 F for 30 minutes
11My Mother NEVER put sugar in the crust. There is usually so much sugar in the filling that there is no need for it in the crust, too. Sugar in the crust would also make the edges burn faster, so just leave it out and save yourself the trouble. Mom never had to cover the edges of her beautiful pies, because there was no sugar in the crust to make them burn faster.