Put milk, marg and flour into a small saucepan.

Turn the heat to medium and whisk briskly and constantly. Keep whisking fast as the marg melts and the sauce comes to a boil - the flour will disappear and the sauce will gradually thicken.

Once bubbling, turn heat to the lowest and leave to cook out for 3 mins. If a little thick, add a touch more milk.

Add salt and pepper.

Take off heat and stir in parsley.