6 T butter, plus 2 more T for topping
2 yellow onions, cut in half and then sliced
4 medium zucchini, sliced 1/4 inch thick
1 1/2 t kosher salt
1/2 t pepper
1/4 t ground nutmeg
2 T flour
1 cup hot milk
3/4 cup bread crumbs (I used Italian seasoned bread crumbs)
3/4 cups grated Gruyere cheese (I used a combination of Parmesan, asiago and Romano)
Preheat oven to 400.
Melt the butter in a large (12 inch) saute pan and cook the onions over low heat for 20 minutes or until they are tender but not browned.
Add the zucchini and cook, covered for about 10 minutes or until they are tender. Add the salt, pepper and nutmeg and continue cooking for a few more minutes.
Stir in the flour and then add the HOT milk. Cook over low heat until it makes a sauce, this takes a few minutes.
Pour the mixture into a 9x13 pan .
Combine the bread crumbs with the shredded cheese and sprinkle over the top of the zucchini. Dot this with the remaining 2 T butter that has been cut into small bits.
Bake at 400 for 20 minutes, or until bubbly and browned.