Preheat the oven to 200C/400F/Gas 6.
Place a baking tray in the oven to heat.
Cut four pieces of greaseproof paper, large enough to hold three pieces of sea bass each, and rub them with olive oil. Sprinkle a little lime zest onto each of the oiled sheets.
Mix the chervil, dill and tarragon together in a small bowl, divide into two sprinkle one half of the herb mixture over the pieces of paper and place three pieces of sea bass on top of each. Season with salt and freshly ground black pepper.
For the lime syrup, place the lime zest and juice into a small non-reactive pan over a medium heat. Add 100ml/3½fl oz water and the sugar, bring to the boil and cook to reduce the liquid by two-thirds, to form a thick syrup. Remove from the heat and leave to cool.
For the apple and lime purée, place the apples into a pan over a low heat and add the lime zest and juice and the sugar. Cook on a low heat, covered, for 8-10 minutes, or until the apples are softened.
Transfer the apple mixture to a food processor and blend until smooth, then pass through a fine sieve.
For the lemongrass sauce, place the fish stock into a saucepan over a high heat and boil to reduce the liquid volume by half.
Add the double cream and four of the lemongrass stalks and continue to cook to reduce the liquid volume by two-thirds.
Place the cream mixture into a clean food processor and add the remaining lemongrass and blend to a smooth purée. Pass the cream and lemongrass sauce through a fine sieve into a small pan. Add a little lemon juice for some sharpness and season, to taste, with salt and freshly ground black pepper.
For the sea bass, season the fish and place the pieces of paper with the sea bass on them onto the preheated tray in the oven. Bake for two minutes, or until cooked through.
To serve, place a spoonful of apple purée onto each plate and smear it slightly with a spoon. Drizzle a trail of lime syrup alongside. Lift the cooked sea bass off the baking paper and place a portion onto each plate next to the purée. Froth the lemongrass sauce with a hand blender and spoon this around. Garnish with a sprinkle of the remaining fresh herb mixture.
