Heat oven to 180C/160 fan/gas 4. To prepare the stuffing mixture, bash the lemongrass with the blunt side of your knife to bruise it, then slice it into thin rings.
Finely slice the ginger (across the grain) – you can leave the peel on. Put all the stuffing ingredients into a bowl and mix together.
Take a piece of baking parchment about 50cm in length and place the 2 sea bass across its width.
Fill the stomach cavities with ¾ of the stuffing mixture, scattering the rest over the fish, then season. Fold the sides of the parchment over the heads and tails of the fish, then roll it into a parcel.
This can now be stored in the fridge for a few hrs, if you like. When ready to cook, place on a tray in the oven and bake for 20-25 mins, until the flesh flakes off the bone.
While the fish bakes, put the new potatoes in cold water and bring to the boil. Once cooked, drain well, slice in half and return to the pan with a knob of butter.
Arrange the new potatoes and sea bass on the plate, still in the parcel, if you like, and sprinkled with the cilantro leaves.