For the hasselback potatoes, preheat the oven to 180C/350F/Gas 4.
Place each potato on a tablespoon and cut slices down through the potato so that you have a fan effect. The edges of the spoon will stop you cutting all the way through.
Season with salt and freshly ground black pepper, to taste, and brush with melted butter.
Place the potatoes onto a baking tray and roast in the oven for 45 minutes or until crisp, basting with the melted butter about halfway through.
For the turbot and the broad bean and wine sauce, place the white wine, stock, saffron and bay leaves in a shallow pan and bring to the boil.
Add the fish, reduce the heat, and poach gently for three minutes.
Meanwhile, for the mushrooms, heat the olive oil in a pan. Add the garlic to the pan and fry for a minute, then add the mushrooms and fry gently. When the mushrooms are cooked all the way through, set them aside, keeping them warm.
Using a fish slice, carefully remove the turbot from the poaching pan and place it on a baking tray. Reserve the poaching liqueur.
For the crust, blend the breadcrumbs, kelp, lemon juice, lemon zest and butter in a blender or food processor. Season with salt and freshly ground black pepper, to taste, and spread the crust over the fish.
Place the fish in the hot oven and cook for about five minutes, or until the crust is golden-brown.
To finish the broad bean and wine sauce, place the peeled broad beans into the fish stock residue and simmer until the liquid has reduced by half.
Add the crème fraîche to the sauce and season with salt and freshly ground black pepper, to taste.
To serve, drizzle the truffle oil over the warm mushrooms, place half of the mushrooms onto each of two plates and arrange the fish portion on top. Drizzle around the broad bean and wine sauce. Place the hasselback potatoes on the side.