Boil the potatoes for 20 mins until
tender. Meanwhile, put the fish in a frying
pan, skin-side down. Stud the onion with
the cloves and put into the pan with the
bay, milk and stock. Bring to the boil, then
cover and simmer for 2 mins. Remove
the cod, which should flake easily, then
re-cover and cook for 3 mins more until
the salmon is just cooked through. Lift
out the fish and set aside. Strain the
In another pan, melt the butter with the
oil, stir in the flour and cook for 2 mins until
it smells toasty. Take off the heat and
slowly whisk in the fish cooking liquid.
Return to the heat, whisk until the sauce
boils and thickens, then stir in the mustard.
Heat oven to 180C/160C fan/gas 4.
Drain and mash the potatoes until
smooth, then beat in the egg yolks,
spinach and most of the cheese. Season
generously with salt, pepper and nutmeg.
Whisk the egg whites to soft peaks, then
fold into the potato in 2 batches.
Flake the fish into a large baking dish,
pour over the sauce and top with the
spinachy potato. Scatter with the rest
of the cheese and bake for 35-40 mins
until golden and risen.