Yields 8 servings (makes one pie)
2 1/2 cups chopped onions
3 tablespoons butter
8 cups chopped mushrooms
1 teaspoon dried thyme
1/2 teaspoon salt
lots of freshly ground black pepper
8 ounces cream cheese
2 1/2 cups unbleached white flour
2 teaspoons baking powder
1/4 teaspoon salt
1 cup butter
1 cup sour cream
flour for coating the dough and board for rolling
1 tablespoon milk
To make the filling, sauté the onions in the butter in a large skillet. When the onions are soft and translucent, add the mushrooms and thyme and sauté for a few more minutes, until the mushrooms release their juices. Add the seasonings. Cut the cream cheese into small pieces and then stir it into the mushrooms until it melts. Remove from the heat and set aside until the crust is ready.
Preheat the oven to 400.
For the crust, combine the flour, baking powder, and salt in a large mixing bowl. Using an electric mixer or by hand, cut the butter just enough to achieve and evenly textured crumbly mix. Stir in the sour cream to form a soft dough. Generously dust the dough with flour and form it into a ball.
On a heavily floured board, roll out 2/3 of the dough to fit a 10-inch pie plate. Trim the edges. Fill with the mushroom mixture. Roll out the remaining dough about 1/4 inch thick (thicker than usual pie crust) and cut into strips 1 inch wide. Weave the strips into a lattice over the filling. This is a bit of trouble but well worth the effort, as you'll see. Fold the ends of the lattice strips under the bottom crust, pinch the edges together, and flute.
For the glaze, beat the eggs and milk. With a pastry brush, thoroughly coat the pie crust. (You'll have more than you need―give leftovers to the cat.)
Bake the pie for 25 to 35 minutes, until the crust is puffy and golden.