Prepare the Oven and Dish: Preheat the oven to 350°F and spray a small 1-quart baking dish with non-stick cooking spray.
Make the Creamy Base: In a mixing bowl, stir together the softened cream cheese, sour cream, mayonnaise, minced garlic, Parmesan cheese, mozzarella cheese, and black pepper until evenly combined.
Add the Vegetables: Stir the chopped, well-drained artichoke hearts and thawed, squeezed spinach into the creamy cheese mixture until the vegetables are distributed throughout.
Fill the Baking Dish: Transfer the mixture to the prepared 1-quart baking dish and spread it evenly across the dish.
Bake the Dip: Place the dish in the preheated 350°F oven and bake for about 20 minutes, or until the dip is heated through and melty.
Serve Warm: Serve the baked spinach artichoke dip warm with tortilla chips, crackers, or toasted baguette slices.