Preheat the oven: Set to 375°F (190°C).
Lightly grease an 8x8-inch or similar baking dish.
Prep the spinach: Thaw completely, then squeeze out as much water as possible. Use a clean kitchen towel or paper towels. Excess moisture will make the dip watery.
Prep the artichokes: Drain well and chop into bite-size pieces. Pat dry with paper towels if they seem wet.
Mix the base: In a large bowl, beat together cream cheese, sour cream, and mayonnaise until smooth.
Season: Stir in garlic, lemon juice, salt, pepper, and red pepper flakes (if using).
Taste and adjust salt and acidity.
Add the veg and cheese: Fold in spinach, artichokes, mozzarella, and Parmesan until evenly combined.
Assemble: Spread the mixture into the prepared baking dish. Top with a light layer of extra mozzarella and a sprinkle of Parmesan for browning.
Bake: 18–22 minutes, until hot and bubbly at the edges. For extra color, broil 1–2 minutes at the end—watch closely.
Rest and serve: Let the dip sit 5 minutes so it sets slightly.
Serve warm with your favorite dippers.