Preheat oven to 375° In a large bowl, spinach and Mix ricotta and cream cheese, salt, pepper and nutmeg. In a microwave-safe bowl, microwave the garlic and olive oil for 20 seconds. Add the garlic and oil to the spinach and cheese mixture.Mix well. Pour 3/4 of the marinara sauce (2 cups) onto the bottom of a 9×13 pan. Using a teaspoon, fill each bowl with the spinach and cheese mixture. Place the stuffed mussels (open side up) in the pan. Cover the pan with aluminum foil and bake at 175° for 25 minutes.Remove the foil and sprinkle the mussels with the breadcrumbs and parmesan. Continue cooking (uncovered) for 10 minutes until the breadcrumbs are golden brown. Remove from the oven and let rest for a few minutes before serving. Just before serving, heat the remaining marinara sauce and pour over the mussels. Add Parmesan if you like.
Enjoy !