Pre-heat the oven at 180ºC. Place the onions cut into pieces, sliced leeks and peeled garlic cloves into the bowl and cook 7 seconds on speed 5.
Use the spatula to scrape the vegetables from the sides of the bowl, add the olive oil and put the lid back on again, and cook for another 7 minutes, at 120ºC on speed 2, without the measuring cup.
Add the thawed and strained shredded codfish and cook 8 minutes, at 100°C on reverse speed 2, without the measuring cup.
Tip the codfish into a tray and set aside.
Without washing the bowl, add margarine, flour and milk. Season with pepper and nutmeg, close the lid and cook 12 minutes, at 90ºC on speed 4.
In a separate bowl, add the codfish and the matchstick potatoes, stir using the spatula and check the seasoning.
Pour the mixture into a tray, top it with the cream and sprinkle with the grated Mozzarella cheese and breadcrumbs. Bake for 40 minutes until topping is sizzling and golden.