Heat the butter in a 10.5" cast iron skillet, once hot add in the garlic and onion. Cook 3-4 minutes until softened

Add in the spinach and cook 3-4 minutes until it's reduced in size. Add in the heavy cream and cream cheese, cook until the spinach is very wilted then stir in the parmesan, a pinch of nutmeg, and season with salt and pepper to taste