In a large mixing bowl, combine the all-purpose flour and salt. Add the chilled butter pieces and use your fingers or a pastry cutter to blend the butter into the flour until the mixture resembles coarse crumbs.
In a small bowl, whisk together the egg, cold water, and white vinegar. Gradually add this mixture to the flour mixture, stirring until a dough forms.
Turn the dough out onto a lightly floured surface and knead for a few minutes until smooth. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
In a large skillet, heat the vegetable oil over medium heat. Add the finely chopped onion and minced garlic, and sauté until soft and translucent.
Add the ground beef to the skillet and cook until browned. Stir in the chopped red and green bell peppers and cook for another 5 minutes.
Add the ground cumin, smoked paprika, ground chili powder, ground black pepper, and salt. Cook for a few more minutes until the spices are fragrant and the peppers are tender.
Remove the skillet from the heat and stir in the chopped hard-boiled egg and green olives. Let the filling cool to room temperature.
Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
On a lightly floured surface, roll out the dough to about 1/8 inch thickness. Use a round cookie cutter (about 4-5 inches in diameter) to cut out circles of dough.
Place a spoonful of the beef filling in the center of each dough circle. Fold the dough over the filling to form a half-moon shape and press the edges together to seal. Use a fork to crimp the edges.
Place the assembled empanadas on the prepared baking sheet. Brush the tops with the beaten egg to give them a golden color when baked.
Bake in the preheated oven for about 20-25 minutes, or until the empanadas are golden brown and crispy.
Allow the empanadas to cool slightly before serving. They can be enjoyed warm or at room temperature.
Enjoy your meal!