Special equipment: a pressure cooker or stockpot
For the stock: Preheat the oven to 375 degrees F. Lightly butter a roasting pan and add the turkey parts in a single layer. Roast until golden brown, 20 to 25 minutes. Cool completely in the pan.
Put the roasted turkey in a pressure cooker with the onion, carrot, celery, garlic, soy sauce and 8 cups water. Lock the lid in place, put over high heat, and bring the cooker to high pressure. Lower the heat to maintain high pressure and cook 15 minutes. Remove from the heat. Let the pressure dissipate naturally, about 2 minutes, or according to the manufacturer's instructions. Remove the lid and skim the stock.
Alternatively put the roasted turkey pieces, the onion, carrot, celery, garlic, soy sauce and 8 cups of water in a stockpot over high heat. Bring to a simmer, reduce the heat to low, and simmer, skimming occasionally, for 2 hours. You should end up with about 8 cups of stock.
Strain the stock through a fine sieve. The stock may be used immediately or cooled and refrigerated for at least 4 hours and up to 24 hours. If refrigerated, the fat will congeal on the top of the stock and should be removed before continuing.
For the cornbread: Lower the oven heat to 350 degrees F. Butter the bottom and sides of a 9-by-13-inch baking dish.
Put the sugar, 5 tablespoons butter and the salt in a stand mixer fitted with the paddle attachment. Beat on medium speed until light and fluffy, 4 to 5 minutes. Beat in the eggs one at a time, waiting until each one is fully incorporated before adding another. Beat in the honey and nutmeg. Reduce the mixer to low speed, add the buttermilk and milk, and beat until incorporated. Add the flour, and beat until well combined. Slowly ¿rain in¿ the cornmeal. Increase the speed to medium and beat until the batter is well-blended and thick, stopping to scrape down the sides of the bowl a few times, 2 to 3 minutes.
Pour the batter onto the prepared baking dish and tap the dish on the counter to settle the batter. Bake until the cornbread springs back lightly when pressed with your finger, 30 to 35 minutes. Cool completely in the dish on a wire rack. The cornbread may be made 3 days in advance, covered with plastic wrap, and held at room temperature.
For the poultry seasoning: Combine the parsley, chervil, rosemary, sage and thyme in a small bowl. Add the celery seeds, coriander, onion powder, salt and pepper. Toss to combine. The seasoning can be refrigerated in an airtight container for up to 3 days.
For the topping: Put the panko breadcrumbs in a medium bowl and add the 3 tablespoons of poultry seasoning (the remainder may be used to season gravies and other holiday dishes). Drizzle with the melted butter and toss with your fingers to moisten the breadcrumbs. Set aside.
For the stuffing: Lower the oven heat to 325 degrees F. Spray a 9-by-13-inch casserole dish with nonstick cooking spray. Cube the cornbread and put into a large mixing bowl.
Heat 2 tablespoons of the olive oil in a large skillet over medium-high heat. Add the sausage and cook, stirring and breaking it up into small pieces with the back of a spoon so it cooks evenly, until cooked through, about 5 minutes. Use a slotted spoon to transfer the sausage to the cornbread.
Return the same skillet with the drippings to medium heat and add the remaining 1 tablespoon olive oil. Once the oil is hot, add the onions and cook, stirring occasionally, until tender and translucent, about 3 minutes. Add the carrots and celery, season lightly with salt and pepper, and cook, stirring, until just tender, 3 to 5 minutes. Add the vegetables to the cornbread and sausage.
Put the eggs in a blender. Put the milk or cream in a medium saucepan over medium-high heat and heat until a thermometer registers 180 degrees F. Add to the blender and mix on low speed until blended.
Add the egg mixture to the cornbread mixture. Add 2 cups of the turkey stock. Reserve the remaining stock for another use. Fold everything together with a rubber spatula until fully combined and the stock has mostly been absorbed. The stuffing will seem a little too wet before baking.
Spread the stuffing in the baking dish. Lightly tap the dish on the counter to even out the mixture in the pan. Add the topping, letting it fall from your fingers in an even layer across the top.
Bake the stuffing until very hot and cooked through, 30 to 35 minutes. Turn the broiler on high, and broil the stuffing until the crust is GBD (Golden Brown and Delicious), 3 to 5 minutes. Serve family-style from the casserole dish
[disclaimer] When blending hot liquids, first let cool for 5 minutes or so, then transfer to a blender, filling only halfway. Put the lid on, leaving one corner open; this will prevent the vacuum effect that creates heat explosions. Cover the lid with a kitchen towel to catch splatters and pulse until smooth.