For marinating the confit duck
Lay the duck legs on a tray, flesh side upwards and distribute the rock salt, crushed pepper, garlic, bay leaves and thyme springs evenly over top. Cling film the tray and leave to marinate in the fridge for approximately 12 hours or overnight.
For cooking the duck
Once the duck legs are marinated, pre-heat the oven to 100°C.
Wash off the marinade with water and pat dry with kitchen cloth.
Place the duck legs skin side down in a large oven proof saucepan and cover with the melted duck fat.
Place the saucepan on a hob on a medium heat and bring the temperature of the duck fat to 85°C. Check the temperature using a food temperature probe.
Place in the pre-heated oven and cook for 2¼ hours until the duck legs are very tender. Using the temperature probe, check the duck fat doesn’t go any higher than 90°C, just under simmering point.
Once cooked, leave to cool in the duck fat and store in the fridge until required.
For the potato, cranberry and Saint Agur gratin
In a small saucepan over a medium heat, bring the whipping cream to a simmer.
Add the salt, pepper and crushed garlic, remove from the heat and set aside to infuse while you prepare the vegetables.
Pre-heat the oven to 160°C.
Layer half of the potato and turnip slices in a large gratin dish and pour over 1/3 of the infused cream through a strainer, ensuring it does not cover the top of the potatoes and turnips.
Evenly spread the cranberry sauce all over, cover with the remaining potato and turnip slices and pour over the rest of the warm infused cream, once again through a strainer.
Cover with foil and bake in the pre-heated oven for 40 minutes.
Remove the foil and continue to bake, uncovered, for a further 20 minutes.
Sprinkle over the Saint Agur blue cheese and continue to bake for a final 10 minutes until golden brown.
Remove from the oven and leave to rest.
To finish and serve
Increase the oven temperature to 220°C.
Remove the cooled duck legs from the fat, making sure to wipe off as much fat as possible.
Place the duck legs on an oven tray, skin side up and roast in the oven for 10-12 minutes until golden all over. Serve with the gratin. Some wilted greens would be a lovely accompaniment to this meal.