01 - Preheat oven to 350°F.
02 - Cut off the top quarter of the sourdough loaf and hollow out the center, leaving a 1-inch thick shell. Reserve removed bread for dipping.
03 - In a large bowl, combine cream cheese, sour cream, mayonnaise, Parmesan, mozzarella, garlic, onion, black pepper, salt, and nutmeg. Mix until smooth.
04 - Fold in the chopped spinach until evenly incorporated.
05 - Spoon the spinach mixture into the hollowed bread bowl. Place the filled bread bowl on a baking sheet.
06 - Replace the top of the bread loosely and bake for 30 minutes, or until the dip is hot and bubbly.
07 - Remove from oven, discard or set aside the top, and sprinkle with fresh chives or parsley. Serve immediately with reserved bread chunks, vegetable crudités, or crackers.