01 - Preheat your oven to 375°F.
02 - In a medium skillet, sauté minced garlic over medium heat for 1 minute until fragrant. If using fresh spinach, add it to the skillet and cook until wilted. Skip this step if utilizing thawed frozen spinach.
03 - In a large mixing bowl, combine softened cream cheese, sour cream, and mayonnaise. Mix thoroughly until smooth and well-incorporated.
04 - Stir in the drained and chopped artichoke hearts, the prepared spinach, ¾ cup of mozzarella cheese, grated Parmesan cheese, kosher salt, freshly ground black pepper, and crushed red pepper flakes (if desired). Mix all ingredients comprehensively.
05 - Transfer the entire dip mixture into a 1-quart baking dish. Smooth the top surface evenly and sprinkle with the remaining ¼ cup of mozzarella cheese.
06 - Bake in the preheated oven for 20 to 25 minutes, or until the dip is hot, bubbly, and its top is golden brown.
07 - Allow the baked dip to cool for 5 minutes before serving. Enjoy warm with tortilla chips, toasted baguette slices, or an assortment of fresh vegetable crudités.