Spinach Quiche (Mom's recipe)

1 box frozen spinach
1 medium onion, chopped
2 Tablespoons butter
5 eggs, beaten
1 cup milk or cream
1/2 teaspoon salt
1/2 teaspoon white pepper
1/2 teaspoon ground nutmeg (or if grating whole nutmeg, grate a scant 1/2 teaspoon)
1/4 cup grated gruyère cheese (really, any cheese will do)
1 uncooked pie shell

Saute onions and spinach in butter until onions are translucent and moisture has evaporated from spinach.  Set aside to cool.  Meanwhile, mix eggs, spices, salt and milk together.  When spinach mixture has cooled sufficiently, add to the egg mixture.  Top with grated cheese.  Pour into pie shell and bake at 400 degrees for 25-30 minutes.