01 - Preheat the oven to 350°F.
02 - In a large bowl, combine cream cheese, sour cream, mayonnaise, mozzarella, Parmesan, garlic, salt, pepper, and nutmeg. Mix until completely smooth and uniform.
03 - Add the drained spinach to the cheese mixture and mix thoroughly until evenly distributed throughout.
04 - Spoon the spinach mixture into the hollowed-out sourdough loaf, packing gently. Alternatively, transfer to a small baking dish.
05 - Place the filled loaf or baking dish on a baking tray. Bake for 20 to 25 minutes until the dip is bubbly and the top develops a golden-brown color.
06 - Remove from oven and serve immediately while hot. Garnish with fresh herbs if desired. Accompany with sourdough bread pieces for dipping.