Make the pecans: Reduce oven to 250 degrees. Line a large sheet pan with parchment or a silicone baking mat. In a mixing bowl, whisk together egg white and water until frothy. Add pecans, salt, sugar, cinnamon, and cardamom. Mix to thoroughly coat pecans in egg white mixture. Place on baking sheet in a single layer. Bake for 45 minutes, making sure to toss nuts with a spoon every 10 minutes. Sugar should crystallize and nuts will be crunchy once they’ve cooled. For garnishing, you can leave them whole or chop them up. (Pecans can be stored in an airtight container for up to 2 weeks.)
Make the cream: Combine cream, sugar, coriander, and vanilla bean in a container. Refrigerate for 2 hours or overnight to steep. Just before serving, strain and whip cream until soft peaks form.
Make the filling: Heat oven to 400 degrees. Slice squash in half lengthwise and place flesh side down on large sheet pan. Roast until fork tender. Scoop out 2 cups of flesh and puree in a blender or food processor until smooth. (Reserve remainder of squash for another use or freeze.) Reduce oven to 375 degrees. To squash, add cream, milk, eggs, sugar, spices, salt, vanilla, and brandy.
Puree or whisk until smooth and pass through a small sieve directly into prebaked pie crust. Bake for 35 to 45 minutes, until slightly puffed and jiggly. Top with whipped cream and sprinkle with pecans.