For the za'atar, mix together all of the za'atar ingredients in a small bowl until well combined.
For the lamb, add the cumin, ginger and honey to the za'atar mixture and mix until well combined. Rub the mixture all over the lamb tenderloin.
Heat the butter in a frying pan over a medium heat. Add the lamb and fry for 6-8 minutes on each side (for medium), or until cooked to your liking. Remove the lamb from the pan and set aside to rest on a warm plate. Reserve any cooking juices left behind in the pan.
For the salsify and wild garlic purée, drain the salsify and place into a pan. Pour over the water and milk and season with salt and freshly ground black pepper. Bring to the boil. Reduce the heat until the mixture is simmering and cook for 20 minutes, or until the salsify is tender. Drain, then place the salsify into a food processor with the butter and cream and blend until smooth.
Heat the oil in a a frying pan until smoking, add the wild garlic leaves and fry for 1-2 minutes, or until just wilted. Stir the wild garlic into the salsify purée and season, to taste, with salt and freshly ground black pepper.
To serve, spoon the salsify and wild garlic purée onto four serving plates. Carve the lamb into thick slices and arrange alongside the purée, drizzling over some of the reserved pan juices.
