Preheat oven to 400 degree F (200 C).

Spread the poultry bones on a large baking pan. Drizzle with the vegetable oil. Toss with a spatula until the bones are evenly coated with oil.

Bake until the bones are nicely charred, 30 to 40 minutes. Remove baking pan from oven and stir the bones once in the middle of roasting.

Transfer all the bones to a large pot. Pour hot water onto the baking pan. Use a spatula to scrape off the brown bits and pour the liquid and brown bits into the pot. Add water to cover bones by 1 inch.

Heat over medium high heat until boiling. Add leek and ginger. Cover, turn to medium low heat, and boil until the meat starts to fall off the bones, 3 to 4 hours. If there is still a lot of liquid left, turn to medium heat and boil, uncovered, until only 4 cups of broth remain. The stock will have turned an opaque light brown color by this point.

Remove and discard all the solid content and drain the soup. Store in airtight container(s) in the fridge for up to 2 weeks or in the freezer for up to 3 months.