1. 1. For the empanada dough: place the flour and salt on the work surface and make a well in the center.
2. 2. Pour in the melted butter and mix gently.
3. 3. Pour in the milk and water, then knead the dough for 15 minutes until smooth. Add a little water if necessary. You can prepare this dough in a stand mixer (using a dough hook).
4. 4. Shape into a ball and let it rest for 30 minutes.
5. 5. Prepare the filling: peel and chop the onions. Finely chop the beef.
6. 6. Heat the oil and butter in a pan, then add the beef and onions. Sauté for 8 minutes over medium heat, then add the peeled and chopped garlic, thyme leaves, cumin, paprika, and chili (according to your taste). Season with salt and pepper. Cook for 2 minutes, then sprinkle with flour and continue cooking for 8-10 minutes. Let it cool completely.
7. 7. Preheat the oven to 375°F (190°C). Cut out dough discs with a diameter of 4-5 inches (10-12 cm), slightly elongate them into ovals, and fill with a little of the prepared filling. Fold the dough over to form turnovers. Seal the edges by pressing with wet fingers. Fold the edges to create small pleats.
8. 8. Beat the egg and brush the empanadas with it. Prick each empanada with a fork. Bake for 20 minutes. Serve warm.