Preheat the oven to 220°C/430°F
MAKE THE BECHAMEL SAUCE:
In a pot on medium-low heat, add the vegan butter. As soon as it melts, add the flour, stir constantly for 2 to 3 minutes. Add the plant-based milk, little by little while stirring constantly.
Add the salt, pepper, the nutmeg, and the nutritional yeast. Stir for 1 minute more, then add the cream. Reserve.
MAKE THE FISHLESS CODFISH:
Shred the oyster mushrooms using your hands. Reserve.
Boil and strain the cubbed potatoes: IMPORTANT: YOU MUST remove them from the heat before they cook completely, the potatoes must be firm because they are going to finish cooking in the oven, and if the potatoes are too soft, they will lose they’re shaped and become mashed.
Add the olive oil to a sauté pan, add the onions, leeks and the bay leaves, stir until they become soft, add the garlic, stir for 40 seconds, then add the shredded oyster mushrooms, the kelp, salt, and pepper and stir to combine and let the mixture cook for about 5 minutes in lower heat, stirring occasionally.
Squeeze half lemon, then add the boiled potatoes and the olives to the mixture then add the bechamel sauce, leaving some for adding on top before putting the cordless fish in the oven.
Remove the bay leaves, add the mixture to a casserole, then add the remainder of the bechamel sauce on top of the mixture, put the casserole for about 30 minutes in the oven, or until the top becomes golden.
Garnish with fresh parsley and some olives.