01 - Heat butter in a large skillet over medium heat. Add chopped onion and cook 2–3 minutes until translucent. Stir in minced garlic and cook 1 minute until fragrant.
02 - Add spinach in batches, stirring until wilted and most moisture has evaporated, approximately 5 minutes.
03 - Pour in heavy cream and add nutmeg, salt, and pepper. Stir to combine and bring to a gentle simmer. Add Parmesan cheese, stirring until melted and sauce is creamy.
04 - Using a spoon, create four wells in the spinach mixture. Crack an egg into each well.
05 - Cover skillet and cook 6–8 minutes until whites are set and yolks remain slightly runny. Extend cooking time for firmer yolks if desired.
06 - Remove from heat and serve right away. Garnish with additional Parmesan cheese if desired.