01 - If using fresh spinach, blanch in boiling water for 30 seconds, then transfer to ice water to stop cooking. Drain thoroughly and chop roughly. For frozen spinach, ensure all excess moisture is squeezed out before use.
02 - Melt butter in a large skillet over medium heat. Add the chopped shallot or onion and cook for 2 to 3 minutes until softened. Add the minced garlic and sauté for an additional minute.
03 - Pour in the heavy cream and whole milk. Bring the mixture to a gentle simmer and cook for 3 to 5 minutes until slightly thickened.
04 - Add the prepared spinach to the skillet, stirring well to coat with the cream mixture. Simmer for 2 to 3 minutes until the spinach is warmed through and fully incorporated.
05 - Stir in the grated Parmesan cheese and nutmeg. Season with salt and black pepper to taste. Simmer gently until the sauce reaches your preferred consistency.
06 - Remove from heat and serve warm as a side dish.