Step 1

Preheat the oven to 425°.

Step 2

In a heavy-bottomed saute pan melt the butter over medium heat. Add the onions and sauté until translucent, about 10 - 12 minutes.

Step 3

Add the flour and nutmeg; cook 2 more minutes, stirring occasionally.

Step 4

Add the milk and cook until thickened, about 5 - 7 minutes.

Step 5

Squeeze as much liquid as possible from the spinach and add the spinach to the sauce.

Step 6

Add 1/2 cup of the Parmesan cheese and mix well. Season to taste, with salt and pepper.

Step 7

Transfer the spinach to a large baking dish and sprinkle the remaining 1/4 cup Parmesan and the Swiss cheese on top.  Bake for 20 minutes until hot and bubbly. Serve hot.