Preheat the oven to 200C/180C Fan/Gas 6. Mix the oil, carrots, celery and chicken wings in a roasting tin. Roast for 45 minutes until the chicken is golden-brown and the vegetables soft.
Put the roasting tin on the hob over a medium heat. Add the white wine, if using, or pour in a glass of water. De-glaze the tin and scrape off any caramelised bits on the bottom of the tin. Remove from the heat.
Use a slotted spoon to transfer the vegetables and chicken to a large saucepan. Stir in the cornflour until combined.
Add the liquid from the roasting tin and the stock. Bring to the boil and simmer for 15-20 minutes. As it bubbles away use a fork to break up the chicken and vegetables as much as you can.
Strain the gravy through a fine sieve into a freezeable container, pushing through as much of the chicken and vegetables as you can. Season, to taste, with salt and pepper.
Allow the gravy to cool completely. Then cover with a lid and transfer to the freezer. (It will keep in the freezer for up to 3 months). Defrost in the fridge the night before you want to serve it.
Reheat in the microwave for 4 minutes on high. Alternatively, if you have the time, add it to the roasting tray when the turkey is resting. Heat gently, and stir thoroughly to incorporate all the flavours from the turkey. Stir well and transfer to a serving jug.