Step 1

Combine flour, sugar, and salt in the bowl of a food processor.  Whirl to combine.

Step 2

Add the cheese and about half of the butter and whirl until no chunks remain. Add remaining slices and whirl briefly to chop them up into pea-sized pieces.

Step 3

Turn food processor on and quickly begin drizzling ice water through the feed tube, stopping before the dough comes together. Pinch some crumbs together between your fingers; if they don’t stick together, add a bit more water and whirl briefly.

Step 4

Turn the mixture out onto a large piece of plastic wrap. Use the plastic wrap to help you bring the dough together; fold the edges of the dough toward the center and press down until it holds together, taking care not to overwork the dough.

Step 5

Divide the dough in half and shape into two flat disks wrapped tightly in plastic wrap. Refrigerate the for at least 45 minutes.

Step 6

Preheat oven to 400° F.

Step 7

On a rimmed baking sheet, toss chopped squash, pear, and sliced garlic with olive oil and salt. Bake until the squash is barely tender, about 10 to 15 minutes.

Step 8

In the meantime, melt the butter in a large sauce pan over medium-low heat. Add the flour and whisk constantly for 2 minutes.

Step 9

Add the broth and whisk until smooth, scraping down the sides with a spatula if needed. Increase heat to medium and whisk in the milk.

Step 10

Stir in leek, thyme sprigs, bay leaf, and paprika. Bring the mixture to a simmer over medium heat, whisking occasionally. Once the mixture begins to bubble, whisk constantly until it thickens, about 3 to 5 minutes more. Whisk in sherry and lemon juice. Set aside.

Step 11

Remove thyme sprigs and bay leaf from the sauce and mix roasted vegetables. Season to taste with freshly grated nutmeg, salt, and white pepper. If preparing ahead, allow the filling to cool to room temperature and refrigerate until ready to use.

Step 12

Increase oven temperature to 425° F. Whisk egg, water, and salt together in a small bowl and set aside.

Step 13

On a lightly floured surface, roll out one of the dough rounds into a 13 to 14-inch circle. Transfer it carefully to the pie dish. Brush some of the egg wash over the dough.

Step 14

Roll out the remaining round into a 13 to 14-inch circle. If using decorative cutters, make vent holes.

Step 15

Brush the overhanging edge of pie dough with some of the egg wash. Center the top crust over the pie dish and seal the pie gently by pressing down all the way around the pie's edge with the bottom of a fork.

Step 16

Trim any overhanging dough with a knife and flute the edge with your fingers, if desired. If not using cookie cutters for vent holes, cut steam vents in the top. Brush the top crust lightly with egg wash.

Step 17

Place the pie on a baking sheet to catch any overflow. Bake for 25 minutes on the bottom rack of the oven. Reduce heat to 350º F and continue baking until the crust turns golden brown, 30 to 40 minutes. Allow the pie to cool for several hours before slicing. Serve warm with Gruyere Mashed Potatoes.