01 - Preheat oven to 350°F.
02 - Slice off the top quarter of the sourdough loaf. Scoop out the center, leaving a 1-inch thick shell. Set aside removed bread for dipping.
03 - In a large mixing bowl, blend cream cheese, sour cream, mayonnaise, Parmesan, mozzarella, garlic, onion, black pepper, salt, and nutmeg until smooth and uniform.
04 - Gently fold chopped spinach into the cheese mixture until evenly distributed throughout.
05 - Transfer the spinach mixture into the hollowed bread bowl. Place on a baking sheet.
06 - Loosely replace the bread top. Bake for 30 minutes until heated through and bubbly.
07 - Remove from oven. Discard or reserve the bread lid. Sprinkle with fresh chives or parsley. Serve immediately with reserved bread pieces, fresh vegetables, or crackers.