For the fish stock, clean the gills of the fish, ensure that there is no blood whatsoever. Heat the olive oil in a large pan. Gently cook the vegetables, add the fish head and bones, 3 litres/5¼ pints of water and a bay leaf. Heat the stock so it is steaming, but do not boil, for 20 minutes. Pass through a sieve and set aside.
For the marmitako, in a large saucepan heat the olive oil. Gently fry the onion and garlic. When half softened, add the red pepper and cook for 2 minutes, then add the padron pepper. When everything is soft add the chilli and tomato sauce.
Cook out the acidity and water of the tomato so that it is almost like a paste. Add the choriceros paste and the wine. Cook off the alcohol for a few seconds and then add the potato chunks and season with salt and pepper. Pour in 200ml/7fl oz of the fish stock and add a bay leaf. It should take around 20 minutes for the potatoes to cook.
Meanwhile in a separate pan, heat until very hot, add 75ml/2½fl oz of olive oil and quickly flash fry the bonito (or tuna) to caramelise it on the outside but keep it raw in the middle.
Once the potatoes are cooked, add the fish to the stew, gently mix it in and take the pan off the heat. Put the lid on and leave it to stand for 10 minutes. After ten minutes give it a gentle shake. Mix the chopped parsley into the stew, drizzle with olive oil and serve.
For the baby gem salad, in a small bowl, mix the olive oil and vinegar until they emulsify, add the shallot and chives and season. Add the piquillo peppers and mix gently so that they don’t break up.
To serve, place a few leaves on a plate and drizzle with the dressing. Place some more leaves on top and drizzle again and so on, so that the leaves remain crisp. Season with salt and pepper.
Serve the marmitako in bowls with the salad alongside.