Preheat your oven to 220ºC/425ºF/gas 7.
Take the top shelf out of the oven and place a baking tray on the middle shelf.
Tear off a metre of kitchen foil. Fold it in half so it’s double thickness, then fold it in half again. You should end up with what looks like a big, foil birthday card. Make two of these then lay them opened and flat on your table. Each foil wrap will hold one piece of fish – you can do a big one for four or a slightly smaller version for two.
In a pestle and mortar, bash your lime leaves until they break down and all the flavour comes out. Then add the lemon grass and do the same again. Do this for a couple of minutes... it’s worth every second. Then add the garlic, chilli, grated ginger and all of the coriander stalks. Once this is all smashed to a pulp, add the soy sauce, the lime zest and juice and the olive old. Mix well, then taste and correct the seasoning with extra soy sauce as you see fit.
Lightly score the sea bass on the skin side with a sharp knife and then rub them with the lime-ginger-lemon grass mix. Allow to marinate for an hour, if you have time, or you can cook it all straight away.
Lightly brush the foil edges with a little beaten egg white – this helps to seal the parcel when you fold it up and keeps all the flavoured steam inside to cook the fish.
Put the portions of sea bass, skin-side up on one side of each envelope. Divide the marinade and all the juice between the two packages and tuck some coriander into the slits of each piece of fish. Fold over the foil, then fold up two sides of the envelopes securely. Just before you seal the final side of the foil bags, divide the sake between the two envelopes, taking care so that it doesn’t dribble out. Pucker and bend the folded sides up so that the juices can’t cook out. Don’t fold the foil right up to the edge of the fish – leave about 2 inches (5 cm) of space all round the fillets to let the steam circulate.
I know all this sounds like a bit of a palaver, but it’s actually dead simple.
Place straight on to the hot tray and cook for about 12 minutes in the preheated oven. Once cooked, allow to sit for 2–3 minutes. Serve the bags at the table – just cut them open and carefully lift out the fish. You can spoon the juices over it (but don’t eat the bits from the marinade as they’re really only there for flavour).
I like to serve this with a bowl of coriander-flavoured rice or noodles, cooked simply. You’re going to love it.