Put the turkey wings (also backbone and neck if you have it) into a small roasting pan and roast them until they are golden brown, about 30 minutes. Heat 3 tablespoons olive oil in a large stock pot over medium-high heat. Add the onion, carrots, garlic, herbs, and peppercorns and cook for 5 minutes. Add the turkey wings. Pour some water into the roasting pan and scrape up all the browned bits on the bottom; add this to the pot. Cover everything in the pot with cold water by 1-inch and bring to the boil, skimming any foam that rises to the surface. Reduce the heat and simmer for about 1 1/2 to 2 hours.
Strain out the solids and discard. Wipe out the pot and put it over medium heat. Melt the butter with the remaining 2 tablespoons olive oil and add the flour. Cook this roux, stirring frequently, until it is golden brown. Slowly whisk in the strained stock being careful to work out any lumps. Cook until the gravy has thickened, about 10 to 15 minutes.