Filled with four kinds of cheese and plenty of tender artichoke hearts, this dip is creamy with a crisp, golden top. Be sure to drain the thawed frozen spinach well to avoid excess water, which can break the cheese sauce.
Preheat oven to 400°F. Stir together cream cheese, Gouda, mozzarella, spinach, artichoke hearts, scallions, mayonnaise, garlic, salt, and cayenne pepper in a medium bowl until smooth. Spoon into a 1-quart baking dish; sprinkle top evenly with Parmesan. Bake in preheated oven until browned and bubby, about 25 minutes. Serve with crostini or tortilla chips.