In a mixing bowl, combine chopped spinach, ricotta cheese, feta cheese, beaten egg, minced garlic, nutmeg, salt, and pepper. Mix well until combined.

Preheat the oven to 400°F (200°C). Roll out the puff pastry on a lightly floured surface and cut into squares or circles.

Place a spoonful of the spinach filling in the center of each pastry piece.

Fold the pastry over the filling and seal the edges by pressing with a fork. Brush the tops with beaten egg and sprinkle with sesame seeds if desired.

Place the pastries on a baking sheet lined with parchment paper. Bake in the preheated oven for 20-25 minutes or until golden brown.

Remove from the oven and let cool slightly before serving.