Preheat oven to 375 degrees Fahrenheit.
Boil spinach until just wilted.
Drain spinach thoroughly using a towel.
Chop spinach finely and set aside.
Melt butter in a sauté pan.
Cook onions until soft and translucent.
Add garlic and cook briefly.
Stir in cream and cream cheese.
Season with salt, pepper, nutmeg.
Fold in chopped spinach gently.
Transfer mixture into baking dish.
Top with grated Parmesan cheese.
Bake until bubbly and golden.
Rest briefly before serving warm.