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

Set the filling aside.

Preheat the oven to 400°F (200°C).

Roll out the puff pastry sheet on a lightly floured surface to smooth it out.

Cut the pastry into squares, approximately 4x4 inches in size.

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

Fold the pastry over to create a triangle and seal the edges by pressing with a fork.

Place the puffs on a baking sheet lined with parchment paper.

Brush the tops with a little beaten egg and sprinkle with sesame seeds if desired.

Bake in the preheated oven for 20-25 minutes or until golden brown.

Remove from the oven and let cool slightly before serving.