An hour before cooking, season the lamb by drizzling with olive oil and sprinkling with sea salt. Press the za’atar into the lamb, cover tightly with clingfilm and leave to get to marinate and get to room temperature.
Heat the oven to 190˚C.
Place a large frying pan over a high heat then place the marinated racks in the pan fat-side down. Cook till golden brown, around 2 minutes then turn and sear for 1 minute.
Put the racks in a large roasting tin, standing them upright with bones interlinked. Add the preserved lemon and rosemary to the tray.
Roast for 8-10 minutes for pink meat and a couple more minutes if you want meat to be medium. Test that the meat it cooked by inserting a metal skewer into the centre of the meat - it should be warm to touch. Cook for a further 2 minutes if it isn’t.
Remove the lamb from the from the oven and transfer to a warmed plate. Cover loosely with foil and allow to rest for 10 minutes.
Blitz everything, except the oil, until smooth.
Continue to blitz whilst adding the oil in a steady stream, until the sauce is thick and glossy. Taste and season accordingly.
