Cut one of the leeks into 0.5cm/¼in thick slices on an angle. Cut the second leek in half lengthways. (Make sure that you don’t cut away the root or dark green part of the leek.)
Heat a heavy-based frying pan until hot. Add the oil and char the leeks cut-side down. Fry for one minute, or until charred.
Season the leeks with salt and cover them with a plate and gently press down. Remove the pan from the heat and set aside.
Score the skin-side of the sole lightly. Season with salt and freshly ground black pepper. Roll each fillet into paupiettes (pinwheels), skin-side facing inside.
Heat the butter in a saucepan. Fry the onion and celery for 2-3 minutes, or until slightly softened.
Add the sole bones, thyme, bay leaf and peppercorns and fry for a further five minutes. Pour in the white wine and then add just enough water to cover.
Make a cartouche (a circle of greaseproof paper) slightly larger than the base of pan. Place it on top of the stock, bring to a boil and then reduce the heat to simmer for 20 minutes.
Strain the stock through muslin and into a clean saucepan. Cook until reduced by half and set aside to cool.
Pour 250ml/9fl oz of the stock into a casserole dish, along with the samphire, leek rings, mussels, the sole and a knob of butter. Season with salt and freshly ground black pepper and cover with a cartouche.
Bring the pan to the boil before placing into the oven to bake with lid on for four minutes. Once cooked, remove the fish and vegetables and keep warm.
Return the pan to the heat and bring to the boil. Cook until reduced by two-thirds, then whisk in the crème fraîche and a little lemon juice. Add the monk’s beard and poach in the sauce for one minute.
Warm the charred leeks gently in the saucepan and then peel off the outer layers to remove any grit.
Place the charred leeks and vegetable oil into a food processor. Season with sea salt and blend until smooth. Strain the mixture though a muslin cloth.
Place the samphire and leeks on the base of a plate and scatter the cooked mussels around. Place two sole fillets on top of the samphire and lay the charred leek over the top. Spoon the sauce over the sauce and drizzle over a little of the leak oil. Finally, garnish with the sea aster.