Step 1: Prepare the Oven and Baking Sheet
Preheat your oven to 400°F (200°C). Line one or two large baking sheets with parchment paper or silicone baking mats. This prevents sticking and makes cleanup easy.

Step 2: Prepare the Spinach
This is the most important step! Thaw frozen spinach completely (microwave for 3-4 minutes or leave in refrigerator overnight). Place thawed spinach in a clean kitchen towel or several layers of paper towels. Twist and squeeze firmly until absolutely no more water comes out—you should extract at least ¼ cup of liquid. Dry spinach is essential for preventing soggy pastry.

Step 3: Make the Filling
In a large mixing bowl, combine the thoroughly dried spinach, softened cream cheese, sour cream, Parmesan cheese, mozzarella cheese, minced garlic, salt, black pepper, and red pepper flakes (if using). Mix everything together with a wooden spoon or spatula until well combined and creamy. Taste and adjust seasoning if needed—add more salt, pepper, or garlic to your preference.

Step 4: Prepare the Puff Pastry
On a lightly floured surface, unfold one sheet of thawed puff pastry. If it has visible seams, gently roll with a rolling pin to smooth them out. Using a sharp knife or pizza cutter, cut the pastry sheet into 12 equal squares (cut into thirds in one direction, then quarters in the other direction, creating a 3×4 grid). Repeat with the second pastry sheet. You should have 24 squares total.

Step 5: Fill the Pastry Squares
Place about 1 tablespoon of spinach dip filling in the center of each puff pastry square. Don’t overfill—too much filling will cause the pastry to burst open during baking or make sealing difficult. Less is more here!

Step 6: Seal the Bites
There are several folding options:

• Triangle fold: Fold one corner diagonally to meet the opposite corner, creating a triangle. Press edges firmly with a fork to seal.
• Envelope fold: Fold all four corners toward the center, overlapping slightly, creating a square packet. Press gently to seal.
• Simple fold: Fold the square in half to create a rectangle. Press edges with a fork to seal.

Make sure edges are sealed well to prevent filling from leaking during baking.

Step 7: Apply Egg Wash (Optional)
For extra golden, shiny tops, whisk together 1 egg with 1 tablespoon of water. Brush this egg wash lightly over the top of each bite using a pastry brush. This step is optional but makes them look more professional. Sprinkle with additional Parmesan if desired.

Step 8: Arrange on Baking Sheet
Place filled and sealed bites on your prepared baking sheet, leaving about 1 inch of space between each one. They will puff up during baking, so don’t crowd them.

Step 9: Bake
Bake in the preheated 400°F oven for 18-20 minutes, until the puff pastry is golden brown, crispy, and fully puffed. The tops should be deep golden and the bottoms should be crisp. If making two sheets, rotate them halfway through baking for even browning.

Step 10: Cool and Serve
Remove from the oven and let cool on the baking sheet for 3-5 minutes—the filling will be very hot! Transfer to a serving platter and serve warm. These are best enjoyed within the first hour of baking while the pastry is still crispy.