1) For the crust: Whisk the flour, salt and herbs together in a medium bowl. Cut in the butter and cream cheese until the mixture is the texture of granola. Add the milk one tablespoon at a time until the dough comes together but is not soggy.
2) Pat the dough into a disk, wrap in plastic and refrigerate at least 30 minutes before rolling out.
3) To roast the vegetables for the filling. Preheat the oven to 425°F. Place the diced, chopped vegetables in a large bowl and drizzle them with the oil. Season with salt and pepper and toss all to coat.
4) Spread the vegetables out on a parchment or foil lined baking sheet and roast in the oven for about 45 to 60 minutes total, stirring well every 15 minutes. The veggies are ready when they are fork tender and caramelized on the edges. Set aside to cool.
5) While the vegetables are roasting, bake or boil the potatoes until they are soft and easily pierced with a fork. Peel, drain and mash the potatoes in a large bowl.
6) Mix the warm mashed potatoes, eggs, herbs, and seasoning together, then fold in the roasted, cooled vegetables.
7) To assemble: Roll the pie crust to a 12" to 14" circle. Drape the crust into a greased 9" or 10" pie pan. Trim and flute the crust edges and place the filling in the unbaked crust.
8) At this point the pie can be well wrapped and frozen for up to 4 weeks. If you are baking now, bake in a preheated 400°F oven for 15 minutes. Reduce the heat to 350°F and bake for another 25 to 30 minutes or until golden browned on top and the center is set.
9) If you have frozen the pie, you can bake it directly from the freezer at 350°F for 1 hour and 20 minutes. Be sure to check the edge of the crust and protect it from burning with a pie shield or foil.