Mix the Tartar sauce and put it aside.
Lay the fish with the bay leaves in a shallow saucepan and pour over the milk. Bring to the boil and poach for 3-4 minutes, under cover. Turn off the heat and rest (still covered) for 10 minutes in the hot milk.
In the meantime, peel & dice the potatoes, then cook them in lightly salted water until tender, then drain.
Carefully remove the fish from the milk using a slotted spatula to a plate and let it cool.
Put the potatoes back in the pan, and crush with a fork over low heat. When you get a dry dough-like texture, turn off the heat. Add the lemon zest, the herbs and 1 Tbsp of the tartar sauce. Taste it, and adjust the seasoning to your liking.
Dry the fish with paper kitchen towel, and add to the potatoes flake-by-flake. Gently combine. Shape 4 patties between your palms. Rest them in the refrigerator for about half an hour or until you’re ready to sue them ( you can freeze them at this point).
Whisk the egg in small bowl. Put some flour and breadcrumbs onto two other plates.
Coat the patties in the flour, then in the egg, then in the breadcrumbs. If you want a thick coating, repeat this step.
Heat some oil in a frying pan and cook the fish cakes in hot oil on both side until golden.
Serve them with the tartar sauce and a crispy salad.