Step 1

In a large bowl, place the flour, xanthan gum, baking powder, and salt, and whisk to combine well. Add the grated, chilled butter, and toss to coat it in the dry ingredients.

Step 2

Add the sour cream, and mix to moisten the dry ingredients with the sour cream. The dough should be shaggy and somewhat crumbly.

Step 3

Knead the dough together with clean hands until it begins to come together. Add ice water by the teaspoon only if necessary for the dough to hold together.

Step 4

Press the dough into a rough disk, wrap it tightly in plastic wrap, and place it in the refrigerator to chill for 30 minutes.

Step 5

Sprinkle the dough lightly with more flour, and roll it out with a rolling pin into a rectangle that is about 1 inch thick, moving the dough frequently and sprinkling it lightly with flour if it begins to stick.

Step 6

Fold the dough over on itself like you would a business letter. Sprinkle the dough again lightly with flour, and roll out it out once again into a rectangle about 1 inch thick.

Step 7

Once or twice more, sprinkle the dough lightly with flour, roll it out, and fold it over on itself like you would a business letter, then wrap it tightly and place it back in the refrigerator to chill for about 2 hours.

Step 8

When the pie dough has nearly chilled completely, preheat your oven to 375° F and locate a 10-inch x 15-inch x 2-inch jelly roll pan. If your pan isn’t nonstick, coat it lightly in cooking oil spray and set it aside.

Step 9

In a large bowl, place the pumpkin puree, eggs, milk, cream, and melted butter, and whisk vigorously to beat the eggs and combine the mixture very well. It should be very smooth.

Step 10

Add the brown sugar, granulated sugar, salt, pumpkin pie spice, and flour, whisking until just combined after each addition. The mixture should be about the consistency of half and half.

Step 11

On a very lightly floured surface, place the chilled pie dough, slice off about 1/4 of the dough and set it aside. Roll out the remaining dough into an 18-inch x 12-inch rectangle. It should be about 1/4-inch thick.

Step 12

Trim any especially jagged edges. Fold the crust in half, and lift it carefully onto the prepared jelly roll pan in the proper orientation and into the edges of the pan.

Step 13

Fold any slightly overhung edges under themselves to secure them, and crimp the edges if you like.

Step 14

Brush the bottom of the crust lightly with the egg white, and place it in the refrigerator to stay cold.

Step 15

Preheat your oven to 375° F.

Step 16

Working with the remaining, small piece of pie crust dough, roll it out about 1/4-inch thick, and cut out small shapes to place on top of the pie crust.

Step 17

You can either bake those shapes alone in a separate pan at 375°F for about 8 minutes or until lightly brown and set, or place them on the pie filling about halfway through baking.

Step 18

Remove the pan with the bottom crust from the refrigerator and fill the crust about 2/3 of the way with the filling mixture.

Step 19

Pull out the oven rack, carefully place the pan on it, and quickly pour the remaining filling into the crust.

Step 20

Carefully return the oven rack to the oven, close the door, and bake for 20 minutes. If you’re adding any shapes to the top of the filling, open the oven and, working quickly, place the shapes on top of the filling.

Step 21

Reduce the heat of the oven to 350°F.

Step 22

Bake until the edges are puffed and set, and the center jiggles only slightly and in a controlled, rather than a loose, way when the pie is shaken from side to side (about another 20 minutes).

Step 23

Remove the pie from the oven and gently press any separately baked pie crust shapes on top, or reserve them for serving on each piece.

Step 24

Place the pan on a cooling rack to cool for at least 45 minutes or until cool to the touch. Cover the pan tightly with plastic wrap and place it in the refrigerator to chill until firm (about 1 1/2 hours). Slice into squares and serve.