01 - Preheat your oven to 375°F.
02 - In a medium skillet, sauté the 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 using thawed frozen spinach.
03 - In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Mix thoroughly until smooth.
04 - Stir in the chopped artichoke hearts, cooked spinach, ¾ cup of the shredded mozzarella, grated Parmesan, kosher salt, black pepper, and crushed red pepper flakes (if using). Mix all ingredients together until well combined.
05 - Transfer the dip mixture to a 1-quart baking dish. Smooth the top surface and sprinkle with the remaining ¼ cup of mozzarella cheese.
06 - Bake for 20 to 25 minutes, or until the dip is hot and bubbly with a golden-brown top.
07 - Allow the dip to cool for 5 minutes before serving. Serve warm with tortilla chips, toasted baguette slices, or fresh vegetable crudités.