Spinach & Cheese Strata

Name: Spinach & Cheese Strata
Prep time: 30 min
Cook time: 1 h 15 min
Total time: 1 h 45 min
Cuisine: Italian
Ingredients: 1 pound bag chopped frozen spinach, thawed and squeezed as dry as possible; 3 tablespoons unsalted butter; 1 large yellow onion, chopped (about 2 cups); 3 garlic cloves, minced; 12 ounces (¾ pound) Italian sandwich bread, cut into 1-inch cubes (about 11 slices or 8 cups); 6 ounces (1½ cups) coarsely grated Gruyère; 2 ounces (⅔ cup) finely grated Parmigiano-Reggiano; 9 large eggs; 2¾ cups half-and-half; 2 tablespoons Dijon mustard; 1¾ teaspoons salt; ¾ teaspoon black pepper; ¼ teaspoon ground nutmeg