For the Arbroath smokie fishcakes, place the Arbroath smokies (or smoked fish) into a large frying pan and pour over the milk. Bring the milk to the boil, then remove the pan from the heat.
Take the smokies out of the milk and set aside to cool. When cool enough to handle, remove as many bones from the fish as possible, flaking and reserving the flesh as you go. Set aside.
Meanwhile, cook the potatoes in a pan of boiling, salted water for 15-20 minutes, or until tender. Drain well and return the potatoes to the pan, then return the pan to the heat for a further minute or two to dry the potatoes out.
Mash the potatoes until smooth using a potato masher or ricer, then mix them in a bowl with the parsley, chives, egg yolk and flaked fish until well combined. Season, to taste, with salt and freshly ground black pepper.
Roll small amounts of the fishcake mixture into balls using your hands, then flatten each slightly to form patties. Chill in the fridge until firm so that they don’t collapse when you fry them.
Sprinkle the flour onto a plate. Beat the eggs in a bowl. Sprinkle the breadcrumbs onto another plate. Dredge each fishcake in the flour, then dip it into the egg, then roll it in the flour until coated.
Heat the olive oil in a large frying over a medium heat. Add the fishcakes for 3-4 minutes on each side, or until crisp and golden-brown on both sides and completely warmed through.
For the sauce, heat a small frying pan until hot, add a knob of the butter and, when melted, fry the shallots for 1-2 minutes, or until softened.
Add the white wine, chicken stock and cream and bring the mixture to the boil. Reduce the heat until the mixture is simmering and simmer until the volume of liquid has reduced by half and thickened.
Strain the mixture through a fine sieve into a clean pan, then whisk in the remaining butter, the lime juice and zest and the chives. Season, to taste, with salt and freshly ground black pepper.
To serve, divide the mizuna leaves among four serving plates. Place the fishcakes on top and spoon some of the sauce over each portion.