Line the bottom of a Dutch oven with some of the cooked potato slices.
For the cooked spinach, heat some olive oil in a pan over medium heat, sauté the spinach and onion, and season with salt and pepper.
For the meatballs, combine the ground beef, onion, parsley, salt, and pepper, and form about 7 meatballs from the mixture. Spread the cooked spinach over the potato slices in the Dutch oven and place the meatballs on top. Line the inner wall of the Dutch oven and the spaces between the meatballs with upright potato slices.
For the white sauce, melt the butter in a saucepan over medium heat and gradually stir in the flour. Add a splash of milk once the mixture starts to dry out, and then once it's smooth again, stir in another splash of milk. Repeat this process until all of the milk is in the saucepan. Let the mixture boil for 2 minutes and then season it with salt, pepper, and nutmeg.
Pour the white sauce over the meatballs in the Dutch oven, crumble the cooked bacon over the sauce, and sprinkle the shredded Swiss cheese on top. Transfer the Dutch oven to a preheated oven and cook at 350°F for 40 minutes.
