Wash the spinach thoroughly and drain well
Chop the spinach if desired
Heat butter or oil in a pan over medium heat
Add minced garlic or onion if using and cook until softened
Add the spinach and cook until wilted
Stir in heavy cream or cooking cream
Season with salt, black pepper, and a pinch of nutmeg if desired
Simmer gently until the sauce thickens slightly
Taste and adjust seasoning
Serve warm