Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or a silicone baking mat.
Roll out the puff pastry sheet on a lightly floured surface. Cut it into 9 equal squares (or smaller if you prefer mini puffs).
Prepare the spinach filling:
In a medium mixing bowl, combine the softened cream cheese, thawed and squeezed spinach, mozzarella cheese, Parmesan cheese, minced garlic (if using), onion powder, salt, and pepper. Stir until well combined and smooth.
Fill the puff pastry:
Place about 1 tablespoon of the spinach and cream cheese mixture in the center of each puff pastry square.
Fold the corners of the square up to meet at the center, or you can fold them into triangles or little pockets, depending on the shape you prefer. Seal the edges by pressing with a fork.
Brush with egg wash (optional):
If you want a golden, glossy finish on your puffs, whisk the egg and brush it over the top of each puff pastry.
Bake:
Place the prepared puffs on the baking sheet and bake in the preheated oven for 15-20 minutes, or until the puff pastry is golden brown and crisp.
Serve:
Let the spinach puffs cool for a few minutes before serving. Serve them warm as a delicious appetizer or snack!
