01 - Set the oven to 350°F to preheat.
02 - In a large mixing bowl, combine softened cream cheese, sour cream, and mayonnaise until smooth.
03 - Add grated Parmesan, shredded mozzarella, minced garlic, finely chopped spring onions, salt, black pepper, and nutmeg; stir thoroughly.
04 - Fold in the well-drained chopped spinach ensuring even distribution.
05 - Spread the mixture evenly into a small casserole or pie dish.
06 - Bake in the preheated oven for 20 minutes until hot, bubbling, and lightly golden on top.
07 - While baking, arrange sourdough bread cubes or slices on a serving platter.
08 - Serve the warm spinach dip immediately alongside the sourdough bread for dipping.