01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - Heat olive oil in a skillet over medium heat. Sauté the diced onion for 3 minutes until softened. Add minced garlic and cook for 1 minute. Stir in chopped spinach and cook until wilted, approximately 2 to 3 minutes. Remove from heat and allow to cool slightly.
03 - In a mixing bowl, combine ricotta, grated cheddar, chopped parsley, dried oregano, ground nutmeg, salt, pepper, and the cooled spinach mixture. Stir thoroughly until well blended.
04 - Roll out the puff pastry sheets on a lightly floured surface. Cut each sheet into 4 equal squares, yielding 8 squares in total.
05 - Place 2 tablespoons of the filling into the center of each pastry square. Fold each square over to form a triangle and seal the edges firmly by pressing with a fork.
06 - Arrange the filled pastries on the prepared baking sheet. Brush the tops with the beaten egg to achieve a golden finish.
07 - Bake in the preheated oven for 18 to 22 minutes, until the pastries are puffed and golden brown.
08 - Allow pastries to cool slightly before serving.