For the yoghurt, spoon the yoghurt into a cheesecloth or muslin cloth placed over a bowl and leave to hang overnight.
Discard the liquid and scoop the yoghurt curd into a bowl. Chill until ready to use.
Place the sugar and 200ml/7fl oz water in a saucepan and heat until the sugar is dissolved. Add the sliced lemon and cook for 15–20 minutes. Set aside to sit overnight in the syrup.
For the braised mutton, mix the salt, chilli, garlic, cumin and coriander together and spread it over the mutton. Set aside to marinate in the fridge for 12 hours.
Wash off the salt mixture. Heat a little oil in a casserole and brown the meat all over. Add both stocks and simmer for around 4 hours or until the meat is tender. Remove the meat from the pan, reserving the liquid, and place on a baking tray lined with baking parchment. Place another sheet of baking parchment on top, followed by another tray and place some weights on top (4 tins of beans will do). Place in the fridge to cool and set.
Strain all the liquid from the pan through a sieve into a clean pan. Heat and reduce in volume to thicken to a sauce consistency. Set aside until needed.
For the mutton ragù, fry both meats in a little oil over high heat. When browned, deglaze the pan with a little water and add the shallots, chilli and garlic. Stir in the cumin and coriander and cook for 30 seconds, then add the tomato purée, chopped tomatoes and brown chicken stock. Simmer for an hour, or until the liquid is thick and glossy. Set aside until needed.
To serve, cut the cucumber into two pieces, about 6cm/2½in long. Take one piece, halve it, halve again and once more so that you are left with eighths. Repeat with the other piece. Slice off the seeded core and discard. Sprinkle with sea salt and set aside.
Char the lettuces on the cut-side down in a hot pan until caramelised. Place them in the reserved mutton sauce and gently warm through.
Preheat the oven to 200C/180C Fan/Gas 6.
When you are ready to serve, slice the mutton shoulder into portions. Brown in a hot frying pan and place in the oven for 6 minutes.
Heat a flat griddle pan. Brush the spring onions with a little oil and griddle for 1–2 minutes until charred and wilted.
In a bowl, mix the feta, mint and honey together.
Place slices of mutton shoulder on serving plates and add a spoonful of ragù, the cucumber and charred lettuce. Dot the feta and strained yoghurt around the plates, and add the confit lemon slices and charred spring onions. Spoon over the sauce.