In a large skillet, heat one tablespoon of olive oil over medium heat. Add the chopped onion and sauté for about 5 minutes until translucent. Stir in the minced garlic and cook for an additional 30 seconds.

Add chopped spinach to the skillet, mixing it into the onion and garlic. Sauté until wilted and bright green, about 2-3 minutes. Remove from heat and let cool slightly.

In a mixing bowl, combine the cooled spinach mixture with ricotta, feta, salt, pepper, and nutmeg. Stir thoroughly to create the filling.

Preheat your oven to 400°F (200°C). Roll out the thawed puff pastry on a floured surface to about ⅛ inch thick, and cut into squares or circles, around 3 inches in size.

Take a spoonful of filling and place it in the center of each pastry piece. Fold and seal the edges with a fork.

Brush the tops with the beaten egg for a golden finish.

Arrange on a baking sheet and bake for 15-20 minutes, until puffed and golden.

Remove from oven and let cool slightly on a wire rack before serving warm.