Gather all ingredients. Preheat the oven to 375 degrees F (190 degrees C). Place turkey legs and wings on a heavy baking sheet, rub lightly with oil, and season with salt, pepper, rosemary, and thyme.
Roast in the preheated oven until golden brown, about 45 minutes. Reserve drippings; discard herbs.
Transfer roasted legs and wings to a large stock pot. Add carrots, celery, onion, and fresh sage. Cover with water approximately 1 inch over the turkey parts and bring to a boil. Reduce to a low simmer and cook until stock is rich in flavor, 3 to 4 hours, skimming occasionally. Strain and discard solids.
Meanwhile, pour apple cider into in a small saucepan and simmer over medium heat until reduced by about half. Set aside.
After roasting the turkey wings and legs, scrape up any browned bits from the baking sheet and transfer those along with any drippings to a saucepan. Add 1/2 cup turkey stock and cook over low heat.
Sprinkle in 3 tablespoons of flour, whisking constantly to form a roux. Cook for 2 to 3 minutes until lightly browned (this prevents a floury taste).
Slowly whisk in 3 cups turkey stock and the reduced apple cider, 1 cup at a time, until smooth and thickened. Simmer gently for 5 to 10 minutes. Season with salt and pepper to taste.
