Spinach and Cheese Strata

I wanted to make this recipe as soon as I saw it on Smitten Kitchen.  I was not disappointed by it.  I accidentally ended up going a little light on the spinach, but it was still a delicious way to start the New Year.  I substituted fresh baby spinach for the frozen stuff.  I used 2/3 of a French baguette, which wasn't exactly 8 cups, but seemed to work out more or less.  Recipe below exactly as it appeared originally (except for the usage of grams!).

Spinach and Cheese Strata (from Smitten Kitchen) (from Gourmet)

Ingredients

1 (10 ounce) package frozen spinach, thawed, squeeze of all excess liquid, and chopped
1 1/2 cups finely chopped onion (1 large)
3 tablespoons unsalted butter
1 teaspoon salt
1/2 teaspoon black pepper
1/4 teaspoon freshly grated nutmeg
8 cups cubed French or Italian bread in 1-inch cubes (1/2 lb)
170g coarsely grated Gruyère (2 cups)
55g finely grated parmesan (1 cup)
2 3/4 cups milk
9 large eggs
2 tablespoons Dijon mustard

1. Sauté onion in butter in a large, heavy skillet over medium heat until soft, about 5 minutes. Add 1/2 teaspoon salt, 1/4 teaspoon pepper and nutmeg and continue cooking for one minute. Stir in spinach, remove from heat and set aside.
2. Spread one third of the bread cubes in a well-buttered 3-quart gratin dish or other ceramic baking dish. Top with one-third of bread cubes,one-third of spinach mixture and one-third of each cheese. Repeat layering twice with remaining bread, spinach and cheese.
3. Whisk eggs, milk, mustard and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper together in a large bowl and pour evenly over strata. Cover with plastic wrap and chill strata for eat least 8 hours or up to a day.
4. The next day, let it stand at room temperature for 30 minutes while preheating the oven to 350°F. Bake strata, uncovered, in middle of oven until puffed, golden brown, and cooked through, 45 to 55 minutes. Let stand 5 minutes before serving.