This recipe has been in my family, passed down from parent to child, at least since half and half was invented. My mother dutifully makes the savory highlight every for every holiday and large family gathering. It's, of course, better with homemade pie crusts, but Trader Joe's or Pillsbury frozen crusts are a great shortcut that take very little away from the pie. —goldzilla
Let 2 pie crusts thaw at room temperature (takes about 20 minutes).
In a skillet, heat the butter and sauté the onion until transparent (about 5 minutes).
Add mushrooms to sauteed onions and sauté about 4 minutes, stirring.
Stir in flour, add half and half and bring to a boil, stirring.
Stir in wine, salt & pepper. Then remove from heat and let cool for about 5 minutes.
Turn out one of the pie crusts onto a Pam-sprayed cutting board or wax paper. Tough to do without breaking the pie crust but try to keep it as whole as possible. Breaks can be fixed by moistening finger with water and then pressing the broken sides together. Flatten out the crust as best you can and then, with sharp knife, cut into 1/2" strips to use as top crust.
Turn mushroom mixture into the second pie crust. Then arrange the 1/2" pastry strips over the top of the mushroom mixture in a lattice fashion (I do all going one way, then all going the other way instead of the very time consuming under- & overlapping). With each strip, lay it down first, then moisten each end and press it into the rim of bottom crust to fasten it.
Once all strips are in place, carefully stand the pastry rim up inside the edge of the pan and flute with your fingers.
Dilute raw egg with a little water and, with a pastry brush, brush the lattice strips for a glazed top.
Bake on lower shelf of oven until crust is brown, about 20 minutes.