Mix the flour and parsley in a wide, shallow bowl. Whisk the eggs, milk and some freshly ground black pepper together in a separate bowl.
Heat the oil in a deep, heavy-based saucepan until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Dip the mushroom slices in the egg mixture, then coat with the flour mixture.
Carefully place the mushrooms into the oil and fry for 3-4 minutes, or until golden-brown. (You may need to do this in batches. Do not overcrowd the pan.)
Remove the mushrooms from the oil with a slotted spoon and set aside to drain on kitchen paper.