01 - Preheat oven to 350°F for baking the filled bread bowl.
02 - Cut a circular opening in the top of the sourdough loaf and remove the lid. Scoop out the soft center, maintaining approximately 3/4 inch of bread along the sides and bottom to create a sturdy bowl. Set aside the removed bread for cubing.
03 - In a large mixing bowl, combine cream cheese, sour cream, mayonnaise, shredded mozzarella, grated Parmesan, minced garlic, chopped onion, salt, black pepper, and nutmeg. Beat until completely smooth and uniform.
04 - Add the well-drained spinach to the cheese mixture. Fold thoroughly until spinach is evenly distributed throughout the base.
05 - Transfer the spinach mixture into the hollowed bread bowl, pressing gently to eliminate air pockets. Position the filled bowl on a parchment-lined baking sheet.
06 - Cover the bread bowl loosely with aluminum foil. Bake for 20 minutes to heat through without excessive browning.
07 - Remove the foil and continue baking for 5 minutes, until the surface becomes golden brown and bubbly.
08 - While the dip bakes, cut the reserved sourdough pieces into uniform 1-inch cubes for serving.
09 - Transfer the warm bread bowl to a serving platter. Arrange the toasted bread cubes and fresh vegetable crudités around the bowl for immediate dipping.