Preheat the oven to 400 degrees. Peel and dice the squash and toss it in the olive oil and brown sugar. Line a baking tray with foil and spread the squash on it. Roast for 20-30 minutes, stirring once midway through. Squash should be tender, and a fork should easily pierce it. Let the squash cool and puree it in a food processor or blender until smooth. The squash will keep for up to a week in the refrigerator or can be frozen.
For the pie
Preheat the oven to 325 degrees
Roll out the pie crust and place in the freezer while you make the pie filling. (For instructions on how to make a pie crust check out my previous post, All About Pie: The Pastry)
Whisk together the brown sugar, eggs and egg yolk, bourbon, vanilla, and salt. Stir in the squash puree and whisk until smooth. Stirring constantly, add the cream in a slow stream until everything is well combined.
Pour into the pie crust and bake for 60-75 minutes until the edges are set and the center barely moves when jiggled.
Optional: Roll out the pastry scraps and cut shapes with a small cookie cutter. Place on a parchment lined cookie sheet, brush with the reserved egg white and sprinkle with sugar. (Demerara sugar is best!) Bake in same oven with the pie for 15-20 minutes until the pastry is cooked and golden brown. Cool until the pie comes out of the oven and carefully place on the surface of the hot pie.