Preheat the oven to 350 F and position a rack in the upper third of the oven.
Spray a baking dish with the nonstick cooking spray.
Put the cream cheese, sour cream, mayonnaise, and garlic in a large bowl.
Mix with an electric mixer until combined.
Add the spinach to the cream cheese mixture, breaking it up as you add it.
Add the artichokes, mozzarella, and about ½ cup of the Parmesan, mixing to combine.
Season with salt and pepper to taste.
Transfer the mixture to the prepared baking dish and top it with the remaining ¼ cup Parmesan.
Place in the oven, and bake for about 20 to 25 minutes, or until the dip begins to bubble.
Turn the oven to broil and continue to cook, keeping an eye on it so it doesn’t burn, until the top is golden brown, about 5 to 7 minutes.
Serve warm with crackers, chips, or toasted bread.
