Spinach Gratin

Ingredients

• 4 T (1/2 stick) unsalted butter
• 4 C chopped yellow onions (2 large)
• 1/4 C flour
• 1/4 t nutmeg
• 1 C heavy cream
• 2 cups milk
• 3 pounds frozen chopped spinach, defrosted (5 (10-ounce) packages)
• 1 cup freshly grated Parmesan cheese
• 2 t salt
• 1/2 t pepper
• 3/4 cup grated Gruyere cheese

Directions

1.     Preheat the oven to 425 degrees F.
2.     Melt the butter in a heavy-bottomed saute pan over medium heat. Add the onions and saute until translucent, about 15 minutes. Add the flour and nutmeg and cook, stirring, for 2 more minutes. Add the cream and milk and cook until thickened.
3.     Squeeze as much liquid as possible from the spinach and add the spinach to the sauce.
4.     Add 1/2 cup of the Parmesan cheese and mix well. Season, to taste, with salt and pepper.
5.     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.