Prepare the Spinach

1. Preheat Oven: Preheat the oven to 375°F (190°C) and grease a baking dish.
2. Cook Fresh Spinach: If using fresh spinach, sauté it in a large skillet with a tablespoon of butter until wilted. Drain excess moisture.

Make the Cream Sauce

1. Sauté Onions and Garlic: In the same skillet, melt the remaining butter over medium heat. Add the chopped onion and cook until translucent, about 5 minutes. Stir in the minced garlic and cook for an additional minute.
2. Add Cream and Seasonings: Pour in the heavy cream and bring to a gentle simmer. Stir in the Parmesan cheese, salt, pepper, and nutmeg (if using) until the cheese has melted and the sauce is smooth.

Combine and Bake

1. Mix Spinach and Sauce: Add the cooked spinach to the cream sauce, stirring until well combined.
2. Transfer to Baking Dish: Pour the spinach mixture into the prepared baking dish, spreading it evenly.
3. Add Toppings: Sprinkle the Gruyère cheese over the top. If desired, add breadcrumbs for extra crunch.
4. Bake: Bake in the preheated oven for 25-30 minutes, or until the top is golden and bubbly.
5. Cool Slightly: Remove from the oven and allow to cool for a few minutes before serving.