Foryoueats: Spinach & Cheese Strata

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