Pour yourself a glass of Head Red GSM 2015 (which can be found in The Drinks List’s Christmas Survival Kit!).
Combine lemon zest, garlic, za’atar, and 3 tablespoons of olive oil together and massage well into lamb shoulder. Cover marinated shoulder tightly with cling film and refrigerate overnight.
Preheat oven to 90 degrees Celsius.
Remove cling film from shoulder and place in a heavy roasting tray and roast for 11 hours.
To make the labneh, add a pinch of salt to the yogurt and mix well. Transfer mixture to a small bowl lined with a chux cloth. Refrigerate for the entire time the lamb is cooking. At the end of the process, discard any excess liquid that has gathered in the bowl, and set aside.
With one hour to go, baste the lamb shoulder regularly with cooking juices from the tray until the cooking time is complete. Remove tray from oven and cover with foil, and set aside.
Meanwhile, add peas, basil, mint, pecorino, and lemon juice to a food processor. Pulse to combine. Stop the motor and add a few decent slugs of olive oil and a pinch of sea salt. Process to combine, being careful not to blitz the mixture too hard. You want to keep some texture.
Serve the lamb either as whole shoulder, which will come apart easily with a pair of tongs, or as individual portions together with smashed peas, a good dollop of labneh and lemon wedges.