Prepare the turkey parts: Thaw the turkey parts in the fridge for a day or two before you begin.

Roast the turkey parts: Preheat your oven to 400°F (200°C). Arrange the thawed turkey parts on a sheet pan and lightly coat them with a high-heat oil. Roast in the oven for 1 to 1.5 hours, or until the turkey parts are golden brown.

Prepare the vegetables: Slice the top green parts off the leeks and clean them. Cut the onion and garlic in half, leaving the skins on for added depth of flavor. Roast the veggies in the same pan for about 30 minutes until caramelized.

Simmer the stock: In a large 6-quart stock pot, add the roasted turkey parts. Cover them with cold water. Bring the water to a boil over medium-high heat, skimming off any scum that rises to the top. Reduce the heat to low and let the stock simmer gently.

Add the vegetables and herbs: Add the roasted leeks, onion, garlic, and any herbs you're using. Also, add the bay leaves and peppercorns. Let the stock simmer for 3 hours, stirring occasionally.

Strain the stock: After 3 hours, remove the stock from the heat. Use tongs or a slotted spoon to remove the turkey parts and vegetables from the pot. Pour the stock through a fine mesh strainer into a clean bowl or large container.

Cool the stock: Allow the stock to cool to room temperature, then refrigerate overnight to fully chill.

Freeze the stock: Once the stock has chilled and gelled, you can freeze it for later use.