Preheat the oven to 170C/150C Fan/Gas 3. Season the turkey drumstick all over with salt and pepper.
Heat the oil in a flameproof, lidded casserole over a medium heat. Add the turkey drumstick and fry for 4-5 minutes, turning regularly until lightly browned on all sides. Transfer to a plate and set aside.
Chop the carrots and celery into roughly 2.5cm/1in lengths. Add the onion, celery and carrot to the casserole and fry for 4-5 minutes, stirring regularly. Stir in the herbs and bay leaf and continue to cook for a further 30-40 seconds.
Dissolve the chicken stock cube in the just-boiled water, then pour it into the casserole along with the wine (or extra chicken stock). Stir in the tomato purée and the redcurrant jelly (or cranberry sauce) and return the turkey drumstick to the mixture.
Cover the casserole with the lid and transfer to the oven. Cook for 1½ hours. After 1½ hours, add the new potatoes to the casserole, turn the turkey drumstick over, then replace the lid and continue to cook for a further 1½ hours, or until the turkey is very tender and the meat is falling off the bone.
Remove the turkey drumstick from the casserole and transfer it to a chopping board. Set aside until cool enough to handle. Meanwhile, spoon as much fat as possible from the surface of the casserole.
In a small bowl, whisk the cornflour with a tablespoon of cold water to form a thick paste. Stir this paste into the pot-roast sauce. Heat the sauce until it is simmering and continue to stir until thickened.
While the sauce is thickening, remove the skin from the turkey drumstick, then remove the meat from the bone in large chunks, discarding any bone or sinew.
To serve, spoon the pot-roast sauce into bowls and place equal amounts of the turkey meat on top of each portion. Serve with freshly steamed green cabbage.