In a medium saucepan over high heat, bring 6 cups water, turkey neck, onion, and bay leaves to a boil. Reduce heat to a simmer and cook, undisturbed, 1 hour. Take stock off heat and strain. Discard solids and set stock aside.
With a mortar and pestle, grind pine nuts to a rough paste; or in a food processor, pulse to a rough paste, being careful not to puree. Set paste aside.
Pour fat off pan drippings into a bowl and set aside (reserve juices left in measuring cup). Set roasting pan on top of stove so it spans two burners; turn them to medium low. Add 1/2 cup reserved fat (if you don't have enough, add butter to make 1/2 cup). Whisk in flour. Cook, whisking, until flour is deeply browned and has a nutty aroma, about 3 minutes.
Still whisking, pour in reserved pan juices and reserved stock. Use a wooden spoon to scrape up any browned bits from bottom of pan, then stir in reserved pine nut paste and whisk until gravy is smooth. Raise heat to high and bring to a boil.
Boil until gravy is thick enough to coat the back of a metal spoon, 3 to 4 minutes. Season to taste with salt and pepper. Pour into a gravy boat through a fine mesh strainer, if you like, and serve immediately.
Note: Nutritional analysis is per tbsp.
Keep warm by covering and resting over a pan of barely simmering water for up to 2 hours. Whisk well before serving.