Begin by making mashed potatoes: Boil the potatoes in a pan of water until soft. Mash the potatoes until the lumps are removed. Set to one side.
Place the fish pie mix in a lined baking tray with the onion, white wine, bay leaves, and garlic.
Cover with foil and bake for 15 minutes, allowing to cool for a further 5 minutes. Remove bay leaves.
Mix the cooked fish, onion and garlic in a bowl. Flake the fish into big chunks.
Stir in the remaining chopped herbs and lemon zest, followed by the grated cheese and mashed potato.
Wrap each cube of cheddar with the mixture, rolling in panko breadcrumbs.
Fry each ball in hot oil for 5 minutes until golden all over and finish in the oven for a further 5 minutes. Once cooked, cover with foil and keep warm.
Blanch leeks in boiling water for 2 minutes and drain.
Simmer leeks in a pan with double cream for 5 minutes. Season with salt, pepper and stir in chives.
Divide the sauce across six plates, with a fish cake placed on each.