To make the stock, place all the ingredients into a large saucepan. Boil 100ml/3½fl oz water and pour over.
Heat a frying pan over medium heat. Add the courgette and girolles and cook for a few minutes. Add the remaining vegetables and butter and sweat for a few more minutes. Pour over the stock, bring to the boil and reduce for a few minutes.
In another pan, heat a knob of butter until foaming. Add the turbot and cook for 2– 3 minutes on each side, or until golden brown all over.
Finish the vegetables with a knob of butter to emulsify the stock, add a dash of lemon juice, and some chopped chervil.
To serve, spoon the vegetables into the bottom of a bowl, top with the turbot and scatter over the chive flowers.