Serve this hot or cold. I like to stand with the fridge door open and eat this one. Earthy spinach with cheezy goodness. Super simple. Serve with a small wedge salad or with the Greek lemon soup.
Preheat oven to 350°. Melt butter in large skillet over medium heat. Add onions and sauté until tender, about 8 minutes. Mix in Spinach, salt, pepper, and nutmeg. Sauté until all water in spinach is evaporated, about 3 minutes.
In a medium bowl, combine yogurt, mozzarella, parmesan, and eggs. Add spinach mixture and fold together until well combined.
Place pie crust in 9 inch pie plate. Spoon spinach and yogurt mixture into pie crust. Bake for 40 minutes until the center is set. Let stand for 10 minutes before cutting and serving.