First make the stuffing, place the Mascarpone cheese in a bowl and whisk until smooth, add the chives, Pernod and lemon juice. Drain the crab meat and gently fold into the Mascarpone cheese and season well.
Clean the fish fillets and place a spoonful of crab meat in the centre of each fillet. Wrap them tightly around stuffing, starting at the wide end of the fillet, and secure with wooden cocktail sticks. Place the fish on a greased oven tray and bake in the hot oven for 15 minutes or until the fish flakes easily with fork.
To make the sweet potato purée, bake the potatoes in the hot oven for 30-40 minutes until they are crispy on the outside but soft inside. Remove and leave to cool a little, then peel away the skin and place the orange flesh in a bowl along with the butter and some seasoning and mash or beat until smooth.
To make the oyster velouté, place the butter in a frying pan and sauté the shallots in it until they are soft but not brown. Pour in the fish stock, Vermouth and the oyster juices. Simmer until the liquid has reduced and then add the cream and keep on a low heat until the velouté has reduced to a sauce consistency. Add the lemon juice, season and keep warm until service.
To make the mange tout, gently wash and cut them lengthways, into thin strips. Place the rice wine vinegar, mirin and sugar in a saucepan. Heat gently until the sugar dissolves and bring to just under a boil, then simmer for about 2 minutes, and remove from heat. When cooled, pour the pickle over the mange tout, tossing gently to make sure everything is coated evenly. Keep in the fridge until service.
To serve, place some sweet potato on the plate and put one stuffed fillet of brill on top, then put another fillet alongside and place some pickled mange tout on tout on top. Drizzle with the oyster velouté and serve immediately.