To Make the Marinade: Grind the cloves into a fine powder.
In a small pan over medium heat, fry cloves, coriander, and ginger in 1 stick of butter until the coriander begins to darken and the ginger starts to caramelize.
Add the garlic and onion and fry until fragrant, about 2 minutes.
Transfer the mixture from the pan to the bowl of a food processor. Add sugar and scallions, then process until the ginger in the mixture is finely ground.
Transfer the mixture to a bowl. Add fish sauce and black pepper. Stir to combine.
Take the baking sheet with the turkey out of the refrigerator. Rub the mixture on both the skin and underside of the turkey. Marinate for at least 1 day—ideally 4 days—in the refrigerator.
To Roast the Turkey: Preheat the oven to 375°F.
Remove the turkey from the refrigerator. Take a piece of parchment paper large enough to cover the turkey and rub one side with an entire stick of butter. Place the parchment paper, butter-side down, over the turkey, tucking the paper under the rack so there’s no overhang.
Roast the turkey. After 1 hour, remove the parchment paper and rotate the turkey. Continue roasting, rotating the turkey every 20 minutes to ensure even browning. The turkey is done once its internal temperature reaches 165°F, or about 1 hour after you first rotate the bird.
Remove the turkey from the oven and let it rest on the baking sheet for 20 minutes. Transfer to a serving platter, saving the drippings that have collected on the baking sheet for gravy.
To Make the Gravy Make a turkey stock: Place turkey backbone, turkey neck, onions, celery, and enough water to cover in a medium pot over high heat. Bring to a boil, then reduce to a simmer and cook 2 1⁄2 hours. Strain and set aside.
Meanwhile, deglaze the baking sheet: Pour the turkey drippings from the baking sheet into a cup. Skim and discard the fat, leaving the remaining juices in the cup. Set the baking sheet over medium heat and pour in 1 cup water. Working quickly with a spatula, deglaze the sheet by scraping up the bits of caramelized juice sticking to the pan. Carefully pour the liquid into the cup with the drippings and set aside.
Make a roux: Place the butter and flour in a medium saucepan over medium heat. Whisking continuously, cook until the mixture turns a deep golden color, being sure to work out any lumps in the roux. A smooth roux will result in a smooth gravy.
Add the drippings and deglazing liquid to the pot and bring to a boil, then add 1 1⁄2 cups turkey stock. Bring to a boil, then add heavy cream and again bring to a boil. Continue boiling until the gravy has reduced and is thick enough to coat the back of a spoon. Remove from heat.
Stir in 1 Tbsp. fish sauce. Taste and add up to 2 more Tbsp. if needed. If the sauce is too salty, add more turkey stock. Add the pepper.
Transfer the gravy to a serving bowl or gravy boat and serve with the turkey.