Creamed Spinach Gratin with Toasted Breadcrumbs - The Pollan Family

Ingredients

• Five 10-ounce packages frozen chopped spinach, thawed
• 4 tablespoons (1/2 stick) unsalted butter
• 1/2 cup plain breadcrumbs
• Kosher salt
• Freshly ground black pepper
• 2 cups finely chopped yellow onions
• 2 cloves garlic, minced
• 1/4 cup all-purpose flour
• 1 cup half-and-half
• 2 cups whole milk
• 1 cup shredded Parmesan cheese
• 1/4 teaspoon ground nutmeg
• 3/4 cup shredded Gruyère cheese