Gently fry a pinch of the shallots in a little butter. Add the clams, garlic and cider then cover and steam lightly. Once the clam shells are open pass through a colander reserving the stock (discard any clams that do not open).
Fillet the brill then remove the skin, portion into 140g/5oz fillets.
Blanch the peas in boiling salted water for 1-2 minutes, then refresh in cold water and set aside.
Heat a non-stick frying pan over a low heat. Add a little vegetable oil, salt, pepper and the fish. Cook slowly until golden-brown.
Meanwhile, add a knob of butter and a pinch of shallots to a separate pan. Gently fry until softened, then add the mushrooms and cook for a minute, but do not colour. Add the reserved cooking juices from the cockles and cook until the volume of liquid has reduced by half. Add the cream and crème fraîche and briefly bring back to the boil. Reduce the heat to low.
The fish should be ready to turn over now, so season the exposed side and turn over.
Drop the peas and cockles into the sauce to warm through.
In a sauté pan or a large frying pan, add 50ml/2fl oz water and a knob of butter. When the butter is melted, add the kale and courgettes, plus a little salt and pepper. Stir fry for 2 minutes or until the vegetables are just tender.
Place the cooked fish on serving plates and pile the courgette and sea kale alongside. Put the tarragon into the sauce, taste to check the seasoning and add to the plates. Garnish with dill and edible flowers.