Preheat the oven to 160°C, fan 140°C, gas 3. Peel the potatoes and cut into chunks. Put them into a pan with just enough water and boil until tender. Drain.
Check the fish for bones and then put into another pan and add enough of the milk and water to cover. Add the bay leaf, cover, and bring up to the boil. Lower the heat and simmer for 2 mins. Turn the heat off and leave for 10 mins.
Put the potatoes back into their pan and heat gently for a minute to dry them lightly. Take the pan off the heat and mash. Add the lemon zest, parsley and chives and mix well. You might like to add a little freshly ground black pepper, too.
Take the fish out of the pan and flake into the potato, check for bones as you go. Very gently mix together, don’t mix too much as you don’t want to mash the fish too much.
Divide into about 12 fishcakes. You might prefer to make 8 large for adults (2 each) and 8 small (2 small each) for toddlers.
Freeze half in a freezer container, layering the fishcakes between greaseproof paper. Seal with a tight-fitting lid.
Dip the others in flour – just enough to coat. Heat the butter and oil in a pan and fry until they are just golden, about 3-4 mins on each side. Keep warm in the oven until they are all cooked.