Preheat the oven to 400°F (200°C).
Line a baking dish with parchment paper.
In a large mixing bowl, combine the chopped spinach, artichoke hearts, cream cheese, sour cream, mozzarella, Parmesan, garlic powder, salt, and pepper.
Roll out the puff pastry and cut it into squares about 4x4 inches.
Place a tablespoon of the mixture in the center of each pastry square, then fold the edges over to seal.
Brush the tops with melted butter for extra richness.
Bake for 20-25 minutes or until golden brown.
Remove from the oven and let cool for a few minutes before serving.