01 - Preheat oven to 350°F.
02 - Cut a large circle from the top of the bread loaf and remove the center, creating a bowl. Hollow out some of the inside, leaving a 3/4-inch thick shell. Reserve the removed bread for dipping.
03 - In a large mixing bowl, combine cream cheese, sour cream, mayonnaise, mozzarella, and Parmesan. Mix until smooth.
04 - Stir in spinach, artichoke hearts, garlic, salt, black pepper, and red pepper flakes (if using) until well blended.
05 - Spoon the mixture into the prepared bread bowl. Place the filled bread bowl and bread pieces on a baking tray lined with parchment.
06 - Bake for 25–30 minutes, or until the dip is hot and bubbly and the bread is golden.
07 - Serve immediately, using bread pieces and additional dippers as desired.