Peel and slice half the onion.
Add the sliced onion, peppercorns, bay leaf and nutmeg to the milk in a saucepan. Bring it to a simmer over medium heat, then turn off the burner and let it stand for 10 minutes.
Season the flour with salt and pepper and mix it through in a flat bowl. Dredge each of the cod fillets in the flour.
Add the oil and butter to a skillet heated over medium heat. Fry the fish for 3 to 4 minutes on each side until golden brown.
Strain the infused milk and discard the onion, peppercorns, and bay leaf. Keep the hot milk ready for making the sauce.
Melt the butter in a saucepan. Then add the flour. Stir the butter and flour together over the heat for at least one minute.
Gradually add the hot milk to the roux whisking all the time over medium heat. Bring to simmering point while whisking.
Finely chop the fresh parsley, then add to the sauce and stir it through.
Place each piece fish on a serving plate and cover in parsley sauce.
