Preheat oven to 350 degrees.
Add the sliced onions to the bottom of a 9×13 baking dish.
Pat the turkey necks dry. Drizzle both sides of the necks with olive oil and then sprinkle the spices onto both sides of the necks.
Rub the spices into the necks. Ensure the spices completely cover the necks. Add more spices if necessary.
Place the seasoned necks over the onions.
Cover the dish with foil and bake for 2 hours. While baking if you notice the onions are starting to char, add a little broth to the bottom of the baking dish.
Remove the pan from the oven and remove foil. Remove the turkey necks from the baking dish and set aside.
Reserve the turkey drippings and onions that remain in the baking dish. The turkey drippings will be used in the gravy.
Heat a saucepan or skillet on medium-high heat. Add the butter and olive oil.
When melted, add in the onions and saute for 3-4 minutes until translucent and fragrant.
Add in the flour. Add it in stages and stir continuously to avoid clumping.
Add in the broth, heavy cream, turkey drippings from the pan, smoked paprika, and garlic powder. Stir until the sauce thickens. Return the turkey to the pan with the gravy.
Bake for an additional 30 minutes (uncovered) or until the turkey is tender and reaches a minimum internal temperature of 165 degrees. You can test if the necks have finished cooking by using a meat thermometer.
If you like for your turkey to fall off the bone, add additional bake time and use your judgment.