Zucchini Gratin (The Zucchini Chronicles, part 3)

Here lies my quest to utilize the zucchini bounty coming from our garden.

In my desperation to use up all of these zucchinis, I found this recipe that uses 4 zucchinis in one pass (!!!).  I was really happy with the way it turned out, delightfully creamy, but still relatively healthy as it's made with a small amount of butter, skim milk, and only 3/4 cup cheese for an entire 9x13 pan.  I'll be making this again.

Ingredients:

3 tbsp butter (plus more, if you want extra butter for the topping)
1 large onion, sliced thinly
4 zucchini, sliced into 1/4 inch slices (enough to fill a 9x13 pan)
4 cloves garlic, minced
2 cups milk (I used skim; 2% will be fine)
1 pinch nutmeg
1 teaspoon dried thyme
2-3 heaping tablespoons all purpose flour
1/2 cup bread crumbs
3/4 cup grated Swiss cheese
salt and pepper, as needed

Directions:

Preheat oven to 400 degrees.  Melt butter over medium heat in a large skillet with deep sides (or a Dutch oven).  Add onion, some salt and pepper and stir.  To help soften onions without burning them, add two tablespoons of water, cover, and cook for about 20 minutes, stirring often, and adding water as needed.  In a sauce pan, heat milk, nutmeg, some salt and pepper over low-medium, stirring occasionally. In the mean time, add zucchini to the pan with the onions, adding another tablespoon of water if needed. Stir, and cover.  Cook for 10-15 minutes, stirring occasionally, until zucchini are softened (but not falling apart).  Add garlic, and 2 tablespoons of flour.  Stir to distribute flour.  Pour hot milk over zucchini, and stir gently until it thickens.  If the sauce isn't thick enough, add another tablespoon of flour.  Taste the sauce, and add more salt if needed.  Pour into greased 9x13 baking dish.  Top with cheese, and then bread crumbs.  If you want, add 2-3 more tablespoons cubed butter on the top, to get the bread crumbs brown and crispy.