01 - Set the oven temperature to 350°F and allow it to fully heat.
02 - In a large mixing bowl, blend cream cheese, sour cream, and mayonnaise until smooth and creamy.
03 - Fold in drained spinach, shredded mozzarella, grated Parmesan, minced garlic, onion powder, black pepper, salt, and nutmeg until evenly mixed.
04 - Transfer the mixture into an oven-safe dish, spreading the surface evenly.
05 - Place the baking dish in the oven and cook for 20–25 minutes until the dip is heated through and golden on top.
06 - Slice off the top of the sourdough loaf and hollow out the center to create a bowl, saving the removed bread pieces for serving.
07 - Brush the inside of the bread bowl and reserved bread pieces with olive oil and toast in the oven for 5–7 minutes until lightly crisp.
08 - Spoon the hot spinach dip into the bread bowl and serve immediately with toasted bread pieces and extra sourdough slices on the side.