What's for Supper? Vidalia Onion Pie

From FoodNetwork.com comes this recipe for a very easy and delicious Vidalia onion pie:

Crust:
1 1/2 cups all-purpose flour
1/2 tablespoon sugar
1/2 teaspoon kosher or Hawaiian salt
1/4 cup cold all-vegetable shortening, cut into small pieces
1/4 cup cold unsalted butter, cut into small pieces
Cold water

Filling:
1/4 egg yolk and 1 teaspoon water for egg wash
1/2 cup unsalted butter
2 pounds Vidalia onions, thinly sliced
3 large eggs, beaten
1 cup sour cream
3 tablespoons all-purpose flour
1/4 teaspoon kosher or Hawaiian salt
1/2 teaspoon freshly ground black pepper
Freshly grated Parmesan

For the crust: All ingredients should be cold. Combine all the dry ingredients in a large mixing bowl. Add shortening and butter. Using a pastry blender cut in the shortening and butter until the mixture resembles coarse meal. Drop by drop, add cold water. Mix in with the fingertips, not with the hands as the palms will warm the dough. Continue mixing water in until the dough begins to hold together without being sticky but not crumbly. Place dough in plastic wrap. Fold over plastic wrap and press down to form a disk. This will make rolling out easier after chilling. Finish wrapping in plastic and place in the refrigerator for at least 1 hour.

Lightly spray a deep 9-inch pie pan or an 8 1/2-inch fluted flan pan. Roll out dough and place in pie plate. Return to the refrigerator until filling is ready. Makes pastry for a 9-inch single crust pie.

Preheat oven to 450 degrees F.

For the filling: Brush egg wash on the inside of pie crust. Return to refrigerator until filling is ready. Over medium heat, melt butter. Add onions and saute until translucent. Do not brown. Combine eggs, sour cream and flour. Add onion mixture. Season with salt and pepper and pour into chilled pie crust. Top with Parmesan. Bake for 20 minutes. Reduce oven temperature to 325 degrees F for the last 20 minutes or until center is set.