Frozen spinach: Thaw the spinach, then squeeze out as much of the excess water as you can. Fresh spinach: Boil a pot of water. Add the spinach and cook for about 1 minute. Drain it and rinse it under cool water. Squeeze out excess water. Chop if desired.
In a pot, sauté the butter and onion over medium heat until it's lightly browned (about 5-7 minutes).
Reduce heat (I keep it on medium-low for this step, but you can increase heat as needed). Stir in the garlic, followed by the heavy cream, cream cheese, parmesan, and nutmeg. It will take a few minutes for the cream cheese to melt in. I break it up with my spoon/stir it continuously. The sauce should thicken up as it cooks.
Stir in the spinach and let it heat through. If you want more liquid, add in a splash more cream. If there's too much liquid, you may need to cook the spinach for a few more minutes to reduce the sauce to your liking.
Season with salt & pepper as needed (I am pretty generous with both).
