Preheat oven to 375°F and grease a 9-inch baking dish or cast iron skillet.
In a large bowl, mix together cream cheese, sour cream, and mayonnaise until smooth and well combined.
Squeeze spinach in a clean kitchen towel to remove all excess moisture, then add to the cream cheese mixture along with chopped artichokes, garlic, 1 cup mozzarella, 3/4 cup Parmesan, salt, and pepper.
Spread mixture evenly into prepared baking dish and top with remaining mozzarella and Parmesan cheese.
Bake for 25-30 minutes until hot, bubbly, and golden brown on top.
Let cool for 5 minutes before serving with sliced baguette, pita chips, or crackers.