Firstly, cook the potatoes by placing them in a saucepan and just covering them with cold water. Add the 5g of salt, bring to the boil with a lid on, then turn down to a simmer. Cook for 15 - 20min until fully cooked. Drain and allow to cool before slicing into rounds. Set aside.
To prepare the fennel: remove the tough outer leaves and discard. Slice the fennel, lengthways, using a mandoline or a sharp knife. Bring a pot of water to the boil add 10g of salt per liter. Cook the fennel in this for 4 min. Drain and refresh in cold water. Reserve until needed.
De seed the chilli and dice finely. Peel and slice the garlic as thinly as possible. Remove the zest from the lemon by using a fine grater. Juice the lemon.
Finally, score the fish a couple of times around the thickest part, on both sides.
To makethe bags, cut the foil into 50cm lengths, fold over to make 25cm sqares. Smear each with butter, generously! Place the fish in the middle, cover with a few slices of fennel, add some chilli, lemon zest and garlic slices. Place a few slices of the cooked potato around the fish. Finish with a good knob of butter and season with a pinch or two of salt
Bring the foil over the fish, and fold to seal each side, leaving the top open. Pour some vermouth and lemon juice into each and seal.
Place in a 200 degree oven and cook for 12 to 15 min. The fish is cooked when the flesh comes away easily from the bone when lifted up with a small knife.
Split open each bag and serve.
«Use the freshest fish possible for this dish. To tell if a fish is fresh, it should have bright eyes, deep red gills, be firm to the touch and, above all, should not smell fishy.»