In a large frying pan, heat one teaspoon of butter on medium heat. Add the onions and cook until they are transparent. Add the chopped garlic and cook for around one minute, be vigilant not to burn the garlic or onion.
Now reduce the heat and add the spinach. Sauté over low heat until the vegetables are mushy, stirring often.
Then, add salt and pepper and let it cook for a few more minutes. Take it from the heat and depending on how you want your empanadas filling to be either mix them with the cream cheese with a hand blender, and then add the feta cheese, or simply cut them a little bit with a knife and then combine with the feta cheese for more texture. Both are delicious and simple ways to make those empanadas. Set aside once thoroughly combined.
Empanada Dough
Now is the time for the dough. Sieve the all-purpose flour, salt, and white sugar into a large mixing bowl. Then use your fingers or a hand blender to incorporate the melted butter until the mixture resembles gritty powder with some (approximately pea-size) butter chunks.
In a mixing bowl, whisk together all the egg, vinegar, and water using a fork. Next, whisk in the flour mixture with a fork (the combination will seem scruffy.)
Place the ingredients on a lightly floured surface, collect it all together, and then knead gently with the palm in a stretching motion to develop the gluten in the dough. Form the dough mixture into a flat rectangular plate and set it aside, covered in plastic wrap.
Forming the Empanadas
Take one portion of dough and roll it with the help of a rolling pin. Now fill it with one or two tablespoons of spinach and feta stuffing. Pull the ends together again and seal with a roller or by fingers. When prepared, put them on baking parchment.
Finish filling the remaining dough, and if the dough starts to stiffen at the ends or you're having difficulties closing them, drop your fingers in a bowl of hot water and softly run your finger along the dough's edges to re-moisten them.
Put the filled empanadas in the fridge for 30 minutes, so they can firm up. While the empanadas are firming, preheat your oven to 375°F / 190°C.
Once the oven is preheated, brush the tops of your Spinach and Feta Empanadas with a beaten egg.
Bake the empanadas for 20-25 minutes, until golden brown. Serve immediately and enjoy!