You will need:
3 pounds chopped spinach (frozen or fresh)
4 tbsp (1/ 2 stick) unsalted butter
1 chopped onion
1/ 4 cup flour
1/ 4 tsp grated nutmeg
1 cup heavy cream
2 cups milk
1 cup grated parmesan cheese
1 tbsp salt
1/ 2 tsp black pepper
1/ 2 cheese (cheddar or mild cheddar){{more}}
Method:
Transfer your spinach to a large baking dish or bowl. Set aside. Preheat the oven to 425F. Melt the butter in a heavy-bottomed sauté pan over medium heat.
Add the onions, and sauté 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 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 baking dish, sprinkle the remaining 1/2 cup parmesan and other cheese on top. Bake for 20 minutes until hot and bubbly, Serve hot.