The turkey and vegetables go into the oven, using just 250ml/9fl oz just-boiled water to make the stock, and transfer all the ingredients to a large slow cooker. Cover and cook on high for 5 hours, turning the drumstick and adding the potatoes after 2½ hours. Remove the turkey leg, spoon of the excess fat then add the cornflour mixture to the pot, cover and cook for 5 minutes or until thickened, stirring.
If making this dish in advance, freeze the turkey meat, off the bone, with the sauce and vegetables (but without the potatoes) in a freezer-proof container for up to 3 months. Thaw overnight in the fridge then reheat in a suitable dish in the microwave until piping hot throughout, stirring at least once.