Bring a pan of salted water to the boil and cook the potatoes for 10-15 minutes. Drain and set aside.
Bring a separate pan of salted water to the boil and cook the vegetables, starting with the broccoli, then asparagus, then broad beans and then peas. Cook the broccoli for 8-10 minutes, depending on the size, then add the other vegetables at 2 minute intervals.
For the turbot, heat a frying pan until hot. Add the butter and the fish, skin-side down. Cook over a medium heat for 2 minutes until the skin is crisp and the fish is cooked two-thirds of the way through. Flip over and cook for another minute, then remove from the heat and leave to rest in a warm place for one minute.
For the sauce, heat a frying pan until medium-hot, add the butter and the shallots and fry for a couple of minutes, or until softened, but not browned.
Add the white wine and cook until the volume of liquid has reduced by half, then add the fish stock and cook until reduced by half again. Add the cream and cook once more until reduced by one-third. Strain through a fine sieve into a clean pan, check the seasoning, adding salt and pepper to taste and set aside.
For the vegetables, heat a frying pan and add the oil, once hot add the potatoes cook for 2-3 minutes, then add the vegetables. Add the butter and season with salt and pepper and stir.
Just before serving, return the sauce to the heat and warm until just simmering, then add the champagne and chives and stir through.
Place the vegetables in the centre of a serving bowl and top with the fish. Pour over the Champagne sauce and garnish with chervil.