In a pan over medium heat, sauté onions until fragrant then add garlic and sauté for another 30 seconds.
Add spinach, parsley, cilantro, dill, salt and pepper mixing them all well together. Cook for 3 minutes then remove from heat and let it cool down for 10 minutes.
Stir in one beaten egg and feta cheese.
Preheat oven to 400F. Beat remaining egg in a small bowl.
Cut pastry sheet into 12 equal parts.
Lightly brush the cups of a mini muffin tin with butter or oil, this step is optional just to make sure that the puff pastry will not be stuck.
Press each puff square into the bottom of one muffin tin, fill with the spinach filling and fold pastry over brushing the top with the beaten egg.
Bake in the oven for 25 minutes or until golden brown.
Let it cool slightly before serving.