In Argentina there's a saying that the oven should be hot enough for the empanadas to finish baking by the time the cook recites the Lord's Prayer.Plus: More Beef Recipes and Tips
In a saucepan, combine the shortening, water and salt and simmer over moderately high heat until the shortening melts and the salt dissolves. Sift the flour into a large bowl, make a well in the center and pour in the shortening mixture. Stir until a dough forms; it will be soft and oily. Pat the dough into a 12-inch square, cover and refrigerate until firm, about 1 hour.
In a saucepan, cover the potatoes with water and boil over moderately high heat until tender, about 20 minutes. Drain and let cool, then peel and cut into 1/2 -inch dice.
In a large skillet, heat 1 tablespoon of the oil. Add one third of the sirloin and cook over high heat without stirring until well browned on the bottom, about 3 minutes. Stir and cook until browned all over, about 3 minutes longer. Season with salt and pepper and transfer to a plate. Repeat with the remaining meat, adding 1 more tablespoon of oil before browning the last batch.
In the skillet, melt the butter in the remaining 1 tablespoon of oil. Add the onions and cook over low heat until softened, about 10 minutes. Add the chili powder, red pepper and cumin and cook over moderate heat, stirring, until fragrant, about 3 minutes. Add the water and simmer until slightly reduced, about 3 minutes. Stir in the scallions, browned sirloin and any accumulated juices. Transfer the filling to a bowl and let cool. Fold in the potatoes, olives and eggs and season with salt and pepper.
Preheat the oven to 500°. Cut the dough in half and then cut each half into 9 equal pieces. Shape each piece into a ball. On a lightly floured surface, roll each ball out to a 7-inch round. Moisten the outer edge of 1 round. Scoop a rounded 1/3 cup of filling on one half of the round and fold the other side over the filling. Press the edge down firmly, then fold it over onto itself at 1/2 -inch intervals to seal. Transfer the empanada to a baking sheet. Repeat with the remaining dough and filling; arrange the empanadas on 2 or 3 baking sheets.
Bake the empanadas for about 25 minutes, or until browned. Serve hot or at room temperature, with hot sauce.
The baked empanadas can be refrigerated overnight or frozen for up to 2 weeks; rewarm in a 350° oven.
These spicy, salty, olive-rich turnovers need only a flavorful Argentinean red, such as a Malbec or Cabernet Sauvignon.