In a mixing bowl, combine flour and salt. Cut in the cold butter until the mixture resembles coarse crumbs.
Gradually add cold water, mixing until a dough forms. Shape the dough into a ball, wrap it in plastic wrap, and refrigerate for 30 minutes.
Meanwhile, heat olive oil in a skillet over medium heat. Add chopped onion and garlic, sauté until softened.
Add ground beef or chicken to the skillet, cooking until browned. Season with cumin, paprika, salt, and pepper.
Stir in chopped olives and hard-boiled eggs, then remove from heat and let the filling cool.
Preheat the oven to 375°F (190°C).
On a floured surface, roll out the chilled dough into a thin sheet. Use a round cutter or glass to cut out circles.
Spoon a generous amount of filling onto each dough circle, fold over, and crimp the edges with a fork to seal.
Place the empanadas on a baking sheet lined with parchment paper. Brush the tops with egg wash.
Bake for 20-25 minutes, or until golden brown and crispy.