This is a must in our home at Thanksgiving. It’s rich but oh so good!

Serves 8

4 tbsp (1/2 stick) unsalted butter
4 cups chopped yellow onions (2 large)
1/4 cup flour
1/4 tsp freshly grated nutmeg
1 cup heavy cream
2 cups whole milk
3 lbs frozen chopped spinach (5x 10oz packages)
1 cup (at least) freshly grated parmesan cheese
1 tbsp kosher salt
1/2 tsp freshly ground black pepper
1/2 cup (at least) grated Gruyere cheese

Preheat the oven to 425 degrees F
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.
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.
Transfer the spinach to a baking dish and sprinkle the remaining 1/2 cup Parmesan and the Gruyere cheese on top.
Bake for 20 minutes until hot and bubbly. Serve hot