01 - Preheat oven to 350°F for baking.
02 - Slice off the top portion of the sourdough loaf. Remove the soft interior bread, maintaining a 1-inch thick shell. Set aside the removed bread pieces for dipping.
03 - Combine cream cheese, sour cream, mayonnaise, mozzarella, and Parmesan in a mixing bowl. Whisk until completely smooth and uniform.
04 - Fold in spinach, artichoke hearts, garlic, salt, black pepper, and red pepper flakes. Mix thoroughly to distribute ingredients evenly.
05 - Transfer the mixture into the hollowed bread cavity. Place the filled bread bowl on a baking sheet.
06 - Bake for 25 to 30 minutes until the dip is heated through, bubbling, and the surface develops a light golden color.
07 - During the final 10 minutes of baking, arrange the reserved bread pieces around the bowl for toasting.
08 - Remove from oven and serve hot. Accompany with toasted bread pieces for dipping.