01 - Preheat oven to 375°F (190°C) for baking.
02 - Heat olive oil in a large skillet over medium heat. Add onion and sauté until soft, about 3 minutes. Stir in garlic and cook 30 seconds more until fragrant.
03 - Add spinach to the skillet, season with salt, pepper, and nutmeg if using. Cook until wilted, about 2 minutes, stirring occasionally.
04 - Remove from heat and transfer the spinach mixture to 4 lightly greased ramekins or a single baking dish, spreading evenly.
05 - Make a small well in the center of each ramekin. Crack an egg into each well, keeping the yolk intact.
06 - Drizzle each serving with about 1 tbsp heavy cream and sprinkle generously with grated Parmesan cheese.
07 - Bake for 12-15 minutes, or until the egg whites are just set and yolks are still slightly runny. Adjust time for firmer yolks as preferred.
08 - Let cool for 2 minutes before serving to allow the dish to set slightly.