If you are serving rice, put this on first – you can keep it warm while the other components cook.
Prepare the ingredients for the fish. Cut the shallot in half width-ways and finely slice. Finely slice the chilli, ginger and lime zest into very thin matchsticks – take time to do this carefully, you want thin, delicate pieces.
Cut the lemongrass stalks in half lengthways.
Mix together the fish sauce, lime juice and sugar.
Cut two pieces of parchment paper about 25cm long and lay them flat on a surface. Place four kaffir lime leaves in a row in the centre of each piece and lay a fish fillet on top.
Put the two halves of the lemongrass stalk either side of the fillet and sprinkle the slivers of shallot, ginger, lime zest and chilli across the top of the fillet evenly. Gently spoon over the fish sauce and sugar mixture.
Gather up the edges of the parchment paper over the fish. Twist it at both ends and fold over the edges of the paper in the middle, leaving space between the fish and paper to allow space for steam. Seal the edges well to trap the steam. It should look like this:.
Bake in the oven for 10-13 mins depending on the size of your fillet.
For the lime butter sauce, finely chop the shallot, garlic lime zest. Heat a little olive oil in a small saucepan, gently fry the shallot, garlic and lime zest over and fry over a medium heat until softened but not coloured (about a minute).
Add the white wine and lime juice, bring to the boil and cook for 2 minutes.
Strain through a sieve and return the strained sauce to pan, discarding the rest.
Re-heat over a low heat and add the butter a few pieces at a time. Whisk continuously until all the butter has melted and incorporated into the sauce and season with a pinch of salt.
Once the butter has all been incorporated remove from the heat and cover - don’t let the sauce overheat as this will make the butter clarify (separate) and your sauce will be ruined. You can re-heat it for a moment right before serving.
If you are also serving pak choi, put a large wok on a high heat with a little water and stir-fry the greens for 2-3 minutes stirring continuously.
Remove the fish from the oven and transfer from the paper to a dinner plate using a spatula. Leave the lemongrass and kaffir lime leaves behind. Pour the juices from the bag over the fish. Plate up the rice and vegetables and serve the sauce alongside.
Cooking ahead? The fish can be prepared several hours in advance (up to the end of step 8 and refrigerated). The sauce may split if made ahead however.