Make pastry as directed in a regular 9-in. pie pan. Let cool.
Preheat oven to 350°. Whisk eggs in a large bowl to blend. Add sugars, corn syrup, bourbon, butter, vanilla, and fine salt and whisk until smooth. Roughly chop half the hazelnuts, then stir all of them and the pecans into egg mixture. Pour into pie shell.
Bake until filling is well browned but still a little jiggly when shaken, 45 to 50 minutes. Let cool on a rack at least 3 hours. Sprinkle with flaked salt.
*Oregon hazelnuts are generally far superior to imports. If your market doesn't carry them, order from freddyguys.com. To roast raw hazelnuts and pecans, bake in separate shallow pans at 350° until golden beneath skins, 8 to 15 minutes.
Make ahead: Up to 1 day at room temperature.