01 - Preheat oven to 375°F. Lightly grease a medium baking dish.
02 - In a large mixing bowl, combine softened cream cheese, sour cream, and mayonnaise. Mix until smooth and well incorporated.
03 - Stir in thawed spinach, chopped artichoke hearts, minced garlic, grated Parmesan, and half of the shredded mozzarella. Season with salt, black pepper, and red pepper flakes if desired.
04 - Pour the mixture into the prepared baking dish and spread evenly. Sprinkle remaining mozzarella cheese over the top.
05 - Bake for 20 to 25 minutes, or until the dip is bubbly and the top is lightly golden brown.
06 - While the dip bakes, slice the baguette and lightly toast the slices if desired.
07 - Remove from oven and serve the warm dip immediately with baguette slices for dipping.