SERVES: 8

• 3 pounds frozen chopped spinach, defrosted (5 (10-ounce) packages)
• 4 tablespoons (1/2 stick) unsalted butter
• 1 chopped yellow onion
• 1/4 cup flour
• 1/4 teaspoon grated nutmeg
• 1 cup heavy cream
• 2 cups milk
• 1 cup freshly grated Parmesan cheese
• 1 tablespoon kosher salt
• 1/2 teaspoon freshly ground black pepper
• 1/2 cup grated Gruyere cheese

1. Transfer your thawed spinach to a large baking dish or bowl. Set aside.
2. Preheat the oven to 425 degrees F.
3. Melt the butter in a heavy-bottomed saute pan over medium heat.
4. Add the onions, and saute until translucent, about 15 minutes.
5. Add the flour and nutmeg and cook, stirring, for 2 more minutes.
6. Add the cream and milk, and cook until thickened.
7. Squeeze as much liquid as possible from the spinach, and add the spinach to the sauce. Add 1/2 cup of the Parmesan cheese and mix well. Season, to taste, with salt and pepper.
8. Transfer the spinach to a baking dish, and sprinkle the remaining 1/2 cup Parmesan and the Gruyere on top. Bake for 20 minutes until hot and bubbly. Serve hot.

‘Mad Men’ Week: Creamed Spinach Gratin