Preheat the oven: Begin by setting your oven to 375°F.
Sauté the green onions: In a 10-inch cast-iron or oven-safe skillet, melt the butter over medium-low heat. Add the white and green parts of the chopped green onions (save the dark green tops for later), and cook them for around 5 minutes, stirring frequently, until they are soft and aromatic.
Create the creamy base: Remove the skillet from the heat and stir in the cream cheese and sour cream. Mix well until the ingredients are smooth and evenly combined.
Mix the remaining ingredients: Add the chopped artichoke hearts, squeezed spinach, Parmesan cheese, half of the mozzarella, garlic, and hot sauce to the skillet. Season the mixture with salt and pepper to taste, and stir everything together until thoroughly blended.
Prepare for baking: Spread the mixture evenly across the skillet. Sprinkle the remaining half of the mozzarella cheese on top to create a cheesy crust.
Bake to perfection: Place the skillet in the preheated oven and bake for approximately 20 minutes, or until the dip is bubbling and the cheese is melted.
Broil for extra flavor: Switch the oven to broil and let the top of the dip cook for an additional 2 minutes, just until the cheese begins to brown slightly.
Garnish and serve: Allow the dip to cool for a few minutes. Sprinkle the reserved dark green parts of the onions on top for garnish, and serve warm alongside tortilla or pita chips.