Preheat the barbecue to around 200°C and set it up for direct cooking

Chop off the green part of the leeks and set aside the white parts. Pull apart the green leaves, wash them thoroughly and dry well. Place them on the grill and leave until completely blackened and dried out (about 30 minutes)

Remove, leave to cool, then blitz to a fine powder in a a spice grinder. This leek ash can now be kept indefinitely in an airtight container

Slice the whites of the leeks in half lengthways – do not remove the root as this will keep them together. Place them on a large sheet of foil then drizzle with olive oil and season with salt and pepper. Place the bay leaves on top then wrap up into a loose parcel. Place on the barbecue for 15–20 minutes or until the leeks are soft and tender but still holding their shape

While the leeks are cooking, make the crème fraîche. Stir 1 tablespoon of the leek ash through the crème fraîche, then taste and season with salt

Unwrap the leeks from the foil and place them directly on the barbecue grill. Halve the lemon and lime and place them on the barbecue, cut-side down. Cook both until nicely charred, turning the leeks occasionally (about 10 minutes)

Remove the leeks, lemon and limes from the heat. Squeeze the juice from the charred citrus into a bowl and whisk in the wholegrain mustard. Add the oil and whisk into a dressing. Taste and season with salt and pepper

Slice the leek halves lengthways and dress with the burnt citrus dressing. Add some spoonfuls of the leek ash crème fraîche to the plate then top with the leeks, soft boiled eggs, thyme and feta (if using). Sprinkle with a small pinch of leek ash for an extra smoky flavour