Prepare the Spinach: Blanch the spinach in a large pot of boiling water for 1-2 minutes until wilted. Drain and press out excess water. Chop the spinach once cool.
Cook the Onions and Garlic: In a large skillet, melt the butter over medium heat. Add the chopped onions and cook until soft, about 3-4 minutes. Add the garlic and cook for another minute.
Make the Cream Sauce: Pour in the heavy cream, bring it to a simmer, and cook for 2-3 minutes until it thickens slightly. Stir in the grated Parmesan cheese until melted and smooth. Season with salt, pepper, and nutmeg.
Combine Spinach with Sauce: Add the chopped spinach to the skillet and stir to coat it evenly in the creamy sauce. Simmer for 2-3 minutes to heat through and combine the flavors.
Serve and Enjoy: Taste the creamed spinach and adjust the seasoning as needed. Serve hot as a side dish with your favorite main course.