Peel shrimp. Sauté the onions, but don't let them brown; set aside.

Sauté the mushrooms until they are soft.

Add the sherry and nutmeg, and simmer until the liquid is almost gone; set aside.

Heat the half and half to a simmer; set aside.

In a medium glass or ceramic dish, layer the potatoes, onions, mushrooms, shrimp, breadcrumbs, and Parmesan repeatedly until the potatoes are gone, finishing with a layer of potatoes.

Pour over the half and half, covering the top layer, and cover the dish with its lid.

Bake at 350 degrees F. for 1 hour, then test the potatoes.

If they are tender, sprinkle with breadcrumbs and Parmesan and dot with butter.

Turn heat to 400 degrees F. and cook, uncovered, until brown.