300g frozen spinach
400g can or jar artichoke hearts packed in water
3 medium green onions
120g low-moisture mozzarella cheese
30g Parmesan cheese
225g cream cheese
1 cup sour cream
1/2 cup mayonnaise
1/2 teaspoon kosher salt, plus more as needed
1/4 teaspoon freshly ground black pepper
Finely grated zest of 1 medium lemon
Coat an 8×8-inch oven-safe baking dish or 10-inch cast iron skillet with fat or cooking spray.
Place frozen spinach in a microwave-safe bowl and microwave in 1-minute bursts until defrosted. Drain and rinse with cold water. When cool enough to handle, squeeze all the excess moisture from the spinach. Coarsely chop it. Place the spinach in the cast iron skillet or a large saucepan if using the baking dish. Drain the artichokes and chop into bite-sized pieces. Thinly slice 3 scallions. Add everything to the skillet or saucepan.
Shred mozzarella cheese and grate the Parmesan. Add parmesan and half the mozzarella to the skillet or saucepan. Add the cream cheese, sour cream, mayonnaise, salt and pepper to the skillet or saucepan.
Cook over medium heat, stirring frequently, until the cream cheese is melted and the dip is evenly combined and steaming, about 8 to 10 minutes. Remove the dip from the heat and stir in the lemon zest.
Transfer the dip to the baking dish (leave if in the skillet) and spread into an even layer. Sprinkle with the remaining mozzarella cheese. Broil until the cheese on top is melted golden brown, 3 to 5 minutes.
Serve the dip. Serve warm with crackers, tortilla chips, baguette slices, crostini, or crudités.