Spinach gratin

2 tablespoons butter
1 large onion, chopped
2 tablespoons flour
1/4 teaspoon grated nutmeg
1/3 cup heavy cream
2/3 cup milk
1 1-lb bag frozen spinach, thawed, with all the juice squeezed out
1/2 cup grated parmesan
salt and pepper

Melt the butter in a heavy saute pan over medium heat. Saute the onions 10 minutes or so. Add the flour and nutmeg and cook for another minute. Add the cream and milk and cook until thickened. Add the spinach and the cheese and mix well. Season to taste with salt and pepper.

Transfer to a baking dish, sprinkle more cheese on top, and bake at 425 for 20 minutes or until hot and bubbly. Serve hot.