Step 1: In a large bowl, whisk together the all-purpose flour and 1 teaspoon salt. Add the very cold, cubed butter to the flour mixture.
Step 2: Using your fingertips or a pastry blender, cut the butter into the flour until the mixture resembles coarse meal with some pea-sized pieces of butter remaining.
Step 3: Gradually add 1/2 cup ice water, 1 tablespoon at a time, mixing lightly with a fork until the dough just comes together. Do not overmix. The dough should be shaggy but cohesive.
Step 4: Divide the dough into two equal portions, flatten each into a disk, wrap tightly in plastic wrap, and refrigerate for at least 1 hour, or up to 2 days.
Step 5: In a large skillet, heat 1 tablespoon olive oil over medium-high heat. Add the ground beef and cook, breaking it apart, until browned. Drain any excess fat.
Step 6: Add the chopped yellow onion, chopped red bell pepper, and minced garlic to the skillet. Cook, stirring occasionally, until the vegetables soften, about 5-7 minutes.
Step 7: Stir in the ground cumin, dried oregano, paprika, cayenne pepper (if using), and salt and black pepper to taste. Cook for 1 minute more until fragrant.
Step 8: Pour in the beef broth and tomato paste. Bring to a simmer and cook for 5-10 minutes, allowing the sauce to thicken and the flavors to meld. The filling should be moist but not watery.
Step 9: Remove from heat and stir in the chopped fresh cilantro. Let the filling cool completely before assembling.
Step 10: On a lightly floured surface, roll out one disk of chilled dough to about 1/8-inch thickness. Using a 4-inch round cutter, cut out circles. Re-roll scraps once if needed.
Step 11: Place about 1-2 tablespoons of the cooled filling in the center of each dough circle. Do not overfill.
Step 12: Lightly brush the edges of the dough with a beaten egg or water. Fold one side of the dough over the filling to meet the other side, forming a half-moon. Press the edges firmly to seal.
Step 13: Crimp the edges with the tines of a fork or create a decorative rope pattern by folding and pressing the dough edges.
Step 14: To fry: Heat 2-3 inches of vegetable oil in a deep pot to 350°F (175°C). Carefully lower 3-4 empanadas at a time into the hot oil. Fry for 3-5 minutes per side, or until golden brown and crispy. Drain on a wire rack lined with paper towels.
Step 15: To bake: Preheat your oven to 375°F (190°C). Place the empanadas on a baking sheet lined with parchment paper. Brush with egg wash (if baking). Bake for 20-25 minutes, or until golden brown and cooked through.