Pour away any excess fat from the turkey roasting tin but keep the onion halves (if using our Roast turkey with citrus butter recipe, see 'Goes well with', right). Set the tin over a medium heat, then sprinkle over the flour. Stir with a wooden spoon and cook for 2 mins, turning the onion over in the mixture to extract the flavour. Slowly stir in the wine and stock, adding any juices from the resting turkey. Bring to the boil, scraping the bits from the bottom, then simmer over a low heat for 15 mins. Sieve and season before serving alongside your Christmas turkey.