Pre-heat the oven to 220°C.
Place the duck legs on a trivet sat inside a roasting tray. Roast for 30-40 minutes until the skin is golden brown and the meat is cooked.
Meanwhile, cook the Charlotte potatoes in a saucepan of salted, boiling water for 15-20 minutes until soft and tender.
Melt the butter in a large frying pan set over a medium heat. Sweat the onion for 8-10 minutes, stirring occasionally, until softened. Remove from the heat and set to one side.
Once the potatoes are cooked, drain and leave to cool a little. Mash them with a fork until broken up, then add the olive oil and seasoning. Mash again a little more, making sure you maintain some texture. Cover and set to one side.
Remove the duck legs from the oven and allow to cool a little. Once cool enough to handle, flake the duck meat using two forks. Add to the onions, then add the sultanas and stir well. Spoon the potatoes into individual, cast iron lidded pots. Divide the duck mixture evenly on top. Replace the lids and bake in the oven for 5 minutes to heat through.
Remove and serve immediately.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.