Spinach & Jarlsberg Gratin

Ingredients 4 tablespoons unsalted butter 4 cups chopped yellow onions (2 large) 1/4 cup flour 1/2 teaspoon grated nutmeg 1/4 teaspoon cinnamon 1 cup heavy cream 2 cups milk 3 pounds frozen chopped spinach, defrosted (five 10-ounce) packages) 1 cup freshly grated Parmesan cheese 1 tablespoon kosher salt 1/2 teaspoon freshly ground black pepper 1/2 […]