Place your skewers in water to soak for at least 20 mins before using.
Soak your leeks in cold water for 10 mins to get rid of any grit.
Bring a large saucepan of lightly salted water to the boil.
Blanch your leeks for 3 mins, then drain and allow to cool for 15 mins.
Thread the leeks on to your drained skewers, with the cut sides facing outwards, like a lollipop.
Place them on a baking sheet lined with foil.
For the marinade, place all the ingredients except the nigella seeds in a small blender and blitz until fully combined and emulsified.
Transfer to a small bowl and stir in the nigella seeds.
Use a pastry brush to brush the marinade on to the skewers, ensuring they are all evenly covered.
Preheat your grill to its hottest setting.
Grill the skewers for 15 mins, turning once halfway through, until both sides are blistered and golden.
Place on a serving dish and sprinkle with a pinch of sea salt flakes, then serve with the lime halves on the side.
