Using kitchen paper, dry the lamb and using a sharp knife to pierce small, 2cm deep holes all over the meat to help with absorption of the marinade.
Peel and finely chop 4 garlic cloves and 1 tbsp of fresh rosemary. Transfer to a bowl, mix in the lemon zest, 1 tbsp oregano and 2 tbsp oil; season. This produces the marinade. Rub the mixture all over the lamb, pressing the garlic and herbs into the holes. When omplete, put to one side for now.
1 bulb garlic, 20 g rosemary, 1 large lemon, 2 tbsp dried oregano, 4 tbsp olive oil
Preheat the oven to gas 6, 200°C, fan 180°C. Using a large deep roasting pan, add the potatoes, (cut into 1 inch pieces). Add the remaining garlic cloves and oregano together with the remaining sprigs of rosemary. Squeeze and pour the lemon juice over the potatoes and placing the squeezed halves to the tin. Season with salt and pepper.
1 bulb garlic, 2 tbsp dried oregano, 20 g rosemary
Toss everything together with your hands, pour over the wine and stock, then position the lamb leg in the middle with the potatoes around it. Drizzle over 2 tbsp oil. Wrap the whole tin tightly in foil.
1.5 kg white potatoes, 200 ml dry white wine, 300 ml vegetable stock, 2 kg lamb
Roast for lamb and potatoes for 1 hour. Remove the foil and roast for 30 mins for medium or 50 mins for well done. The potatoes will be ready when tender when pierced with a knife. Make sure the lamb is cooked by inserting a skewer into the thickest part of the lamb for a few seconds. Remove it and if hot then the lamb is cooked. Most of the fluid in the pan should have evaporated by now.
If the potatoes are still quite wet, remove a few spoonfuls of the stock (reserve to make gravy, if you like). Cover the tin loosely with the reserved foil and leave to rest for at least 20 mins. Scatter over the parsley and feta to serve.
100 g feta cheese, 15 g parsley
Notes
If the juices of the leg of lamb are pink when the skewer is withdrawn, the meat will be medium.