In a skillet, heat the olive oil over medium heat. Add the minced garlic and sauté for about 1 minute, or until fragrant.
Add the chopped spinach to the skillet and cook until wilted, about 2-3 minutes. Season with salt, pepper, and a pinch of nutmeg (if using).
In a mixing bowl, combine the cooked spinach and garlic with ricotta, feta, and Parmesan cheese. Mix well until fully incorporated.
Roll out the thawed puff pastry sheet on a lightly floured surface until it's about ¼ inch thick. Cut the pastry into squares or rectangles, approximately 4x4 inches.
Place a generous tablespoon of the spinach mixture in the center of each pastry square.
Fold the pastry over to create a triangle or rectangle, sealing the edges by pressing them together with a fork or your fingers. Brush the tops with the beaten egg for a golden finish.
Place the stuffed pastries on a parchment-lined baking sheet and bake in the preheated oven for 20-25 minutes, or until golden brown and crispy.
Remove from the oven and let cool slightly before serving.
Notes
Serve warm on a wooden board, garnished with fresh spinach leaves and extra Parmesan.