Zucchini Gratin

Recipe by Ina Garten

Ingredients
6 tablespoons (3/4 stick) unsalted butter, plus extra for topping
1 pound yellow onions (3 large), cut in half and sliced
2 pounds zucchini, sliced ¼ inch thick
2 teaspoons salt
1 teaspoon freshly ground black pepper
¼ teaspoon nutmeg
2 tablespoons flour
1 cup hot milk
¾ cup fresh bread crumbs
¾ cup Gruyere cheese, grated

Instructions
– Preheat oven to 400 degrees.
– Melt the butter in a very large (12 inch) saute pan and cook the onions over low heat for 20 minutes, or until tender but not browned. Add the zucchini and cook, covered, for 10 minutes, or until tender. Add the salt, pepper and nutmeg and 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 8×10 inch baking dish.
– Combine the bread crumbs and Gruyere and sprinkle on top of the zucchini mixture. Dot with 1 tablespoon butter cut into small bits and bake for 20 minutes or until bubbly and browned.

&nbs