Place the frozen spinach in a microwave-safe bowl. Cover and microwave on high just until thawed, about 4 minutes.
Place the spinach in a colander and press on it with the back of a large spoon or a spatula to remove as much liquid as possible.
In a medium saucepan, melt the butter over medium heat. Add the garlic and cook for 1 minute.
Stir in the spinach, salt, pepper, nutmeg, heavy cream, and parmesan.
Cook, stirring, just until heated through, 1-2 minutes. Serve immediately.
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Notes
While I'm trying to keep the creamy ingredients reasonable compared to restaurants, it's not a good idea to skimp on them. The butter, cream, and parmesan make this dish into the tasty indulgence it is. So, if the mixture is too dry, don't hesitate to add more cream. You can add up to ¼ cup of additional cream.
Removing as much excess water as humanly possible from the thawed spinach is essential. It's the only way to ensure the creamed spinach is thick, creamy, and not soupy or watery.
You can keep the leftovers in the fridge, in an airtight container, for up to 4 days. Give them a good stir before reheating and serving them, and reheat them gently in the microwave, covered, at 50% power. You can also reheat them on the stove on low heat or in a 250°F oven.