Preheat the oven to 195°C on hot air mode, set to 180°C, 50 minutes. Wash the potatoes well, dry them and prick several times with a fork. Pour some olive oil into your hands and rub over the potatoes. Place on a Retigo bake GN container.
Meanwhile, for the filling, put the milk, garlic and bay in a saucepan, season and bring to a simmer. Add the cod and cook gently for 4 minutes, then remove from the heat. Lift out the cod using a slotted spoon and place on a plate. Pour the milk mixture into a jug.
Let the potatoes cool slightly, then cut them in half lengthways. Scoop out the flesh and put it in a bowl. Flake the cod and add it to the potato. Mix in the parsley. Add 150ml of the milk and mash.
Spoon the flesh back into the potato skins and scatter the cheese on top. Place on the Retigo bake set to 190°C, 0% flap valve and bake for 8 minutes.