Zucchini Gratin with Mushrooms

Preheat the oven to 400°F.

Melt butter in a very large (12-inch) saute pan (use one with a lid—you’ll need it in a minute) and cook the onions over low heat for 20 minutes. Cook them until tender but not browned. Add the zucchini and season with salt and pepper. Put the lid on and cook until tender about 10 minutes. Add the mushrooms and nutmeg. Cook uncovered for 5 more minutes. Stir in the flour. Add the hot milk and cook over low heat for a few minutes, until it makes a sauce.

Pour the mixture into an 8 by 10-inch baking dish. Top the zucchini mixture with the Swiss cheese, to cover it. Top the cheese with the breadcrumbs. Then dot the top with 2 tablespoons of butter cut into small bits. Put dish into the oven and bake for 20 minutes, or until bubbly and browned.