Preheat your oven to 400 degrees F. Grease 4 large ramekins (or small cast iron skillets) with a non-stick spray and place them on a large baking sheet. Set aside.
In a large non-stick skillet over medium heat, add 1/4 cup of water. Add the spinach and cook for about 2 minutes, tossing frequently, until wilted. Transfer to a strainer and press out any remaining liquid. Set aside.
To the same skillet, melt the butter over medium heat. Add the onion and cook until translucent, about 5 minutes. Add the garlic and cook for an additional minute. Add the spinach, heavy cream, mustard and a generous amount of salt and black pepper. Cook for about 5 minutes until warmed through and thick. Remove from heat.
Divide the spinach evenly among the prepared ramekins. Break 2 eggs into each ramekin and sprinkle with mozzarella and parmesan cheese. Bake for about 8 minutes for runny eggs, or cook longer until the eggs are cooked to your liking. Remove from heat and garnish with fresh thyme and bread crumbs. Enjoy!