2 fistfuls curly parsley sprigs, about 25g, plus 2 tbsp finely chopped parsley
olive oil, for browning
1 chicken crown
500g sweet potatoes, peeled
1 onion, sliced
3 garlic cloves
3 tbsp maple syrup
3 tbsp balsamic vinegar
8 outside leaves of a large head of Chinese leaf
6-8 large fresh basil leaves
4 large Cumberland sausages, about 200g
4tbsp vinaigrette, preferably homemade
Mix 125g of the softened butter with the lemon zest and a squeeze of juice. Strip the leaves from 3 of the rosemary and all the thyme sprigs and finely chop with the parsley. Mix the herbs into the butter until smooth. Use your hands to carefully peel back the top-breast skin and slowly push your hands between the flesh and skin until you reach the bottom. Press the butter into the pocket of skin, working it over the flesh, then stretch the skin back over the breast. Smooth down the outside with your fingers. Chill the bird for half an hour or more.
Heat oven to 220C/fan 200C/gas 7 and heat a large, non-stick, ovenproof frying pan until you can see a heat haze rising. Add about 2 tbsp oil and brown the bird all over. Transfer the bird to the oven either in the same pan, if ovenproof, or in a roasting tray and cook for 5 mins. Turn the heat down to 190C/fan 170C/gas 5, then cook for another 30-35 mins, ladling over pan juices every 10 mins to baste. Remove and allow to stand for 10 mins.
Tear off a large sheet of foil and fold in half. Spread the centre with 25g butter and season. Lay 4 Chinese leaves down in a line, pressing on the stems to snap - flatten if necessary. Place the basil leaves over, then lay the sausages tightly down the centre and cover with remaining leaves. Roll in the foil as firmly as possible. Twist the ends of the foil and cut them off or fold them in. Place in a shallow baking tray and add a cup of cold water to help it steam-bake. Cook it on the shelf under the bird for the final 25 mins, then remove and stand for 10 mins before unwrapping and slicing into diagonal chunks.
Cut the sweet potatoes into long wedges, blanch in boiling water for 2 mins, drain, cool in iced water and set aside. Heat a large frying pan until hot and add 3 tbsp oil. Stir-fry the onion, garlic cloves and remaining rosemary sprig for 2-3 mins, then add the sweet potato and remaining butter and saute until lightly browned.
Pour in the maple syrup and cook for 2 mins until it caramelises. Trickle in the vinegar and about 1a„2 cup (120ml) water. Cook for 10 mins, shaking the pan occasionally until the wedges are just tender, then remove the garlic and rosemary. Keep warm.
To serve, first mix the chopped parsley into the vinaigrette. Using a sharp knife, feel for the top of the breast bone and carefully slice away each breast in one whole piece, slashing it in short movements from the rib bone and cutting it away to include the exposed wing-tip bone. Lay on a chopping board and cut into 3 or 4 thick slices. Repeat with the other breast. Divide the sweet potato between 4 warmed plates and arrange the chicken on top. Place the sausage-roll chunks around the edge and spoon over the parsley vinaigrette.