Cook the potatoes in boiling salted water until tender. Allow to cool a little then peel and mash with the butter and hot milk.
Stir in the eggs and two thirds of the parmesan.
While the potatoes are cooking fry the mushrooms and garlic in the butter until golden and sweet. Season with the parsley and some salt and pepper.
Lightly butter a baking dish and spoon half of the potato over the bottom of the dish.Cube the cheese and put it on top.
Scatter the mushrooms and their cooking juices over the cheese and cover with the remaining mashed potato. Sprinkle over the remaining parmesan cheese.
Bake in an oven preheated to 190 C Gas 5 until the crust is golden.