1. Preheat Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
2. Prepare Filling: In a medium bowl, combine the thawed and drained spinach, ricotta cheese, mozzarella cheese, Parmesan cheese, minced garlic, salt, black pepper, and red pepper flakes (if using). Mix until well combined.
3. Assemble Pastry: Roll out the thawed puff pastry sheet on a lightly floured surface. Cut it into squares or rectangles, depending on your preference and size of the sheet.
4. Add Filling: Place a spoonful of the spinach and cheese mixture onto one half of each pastry square or rectangle, leaving a border around the edges. Fold the other half of the pastry over the filling to create a triangle or rectangle shape. Press the edges firmly with a fork to seal.
5. Brush with Egg Wash: Transfer the stuffed pastries to the prepared baking sheet. Brush the tops with the beaten egg, which will give them a golden sheen when baked. Sprinkle with sesame seeds or poppy seeds if desired.
6. Bake: Bake in the preheated oven for 15-20 minutes, or until the pastries are puffed and golden brown.
7. Serve: Remove from the oven and let cool slightly before serving. Enjoy your delicious Spinach Stuffed Pastry as a snack or appetizer!
