For the stock, heat the butter in a saucepan and add the shallot, celery and thyme. Cook for 2-3 minutes. Add the langoustine shells and increase the heat. Add the white wine and fish stock and cook for 5 minutes.
Remove from the heat and place in a large food processor. Blend everything together, including the shells. Pass through a sieve and set aside.
For the sauce, heat a large sauté pan and add the butter. Once melted add the shallot and cook for 1 minute. Add the vermouth, stock and bay leaf and cook until the volume of liquid has reduced by half. Add the cream and reduce by half again. Pass through a sieve into a clean pan. Add the grapes and cucumber balls and cook for 1 minute.
To cook the sole, heat a large frying pan and add the butter. Once hot add the sole. Cook on each side until golden and cooked through. Add the langoustine meat and warm through.
Put the sole fillets on a large plate and top with the langoustines. Pour the sauce around the plate and garnish with the fresh chervil and edible flowers.