01 - In a large bowl, combine flour and salt. Add cold, cubed butter and rub with fingertips until mixture resembles coarse crumbs. In a small bowl, whisk egg, cold water, and vinegar together, then add to flour mixture. Stir until just combined and knead lightly to form a smooth dough. Wrap tightly in plastic and chill for at least 30 minutes.
02 - Heat olive oil in a skillet over medium heat. Sauté onion for 3 minutes until softened. Add garlic and cook for 1 minute more. Add ground beef, breaking up with a spoon, and cook until browned. Stir in corn kernels, cumin, smoked paprika, oregano, chili powder, salt, and pepper. Cook for 2 additional minutes, then remove from heat and allow to cool slightly. Fold in shredded cheddar and mozzarella cheeses.
03 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
04 - On a floured surface, roll the chilled dough to about 1/8-inch thickness. Cut into 5-inch diameter circles. Place approximately 2 tablespoons of filling in the center of each circle. Fold dough over to form a half-moon shape and press edges with a fork to seal.
05 - Place empanadas on the prepared baking sheet and brush the tops with the beaten egg wash.
06 - Bake for 20 to 25 minutes until empanadas are golden brown and crisp. Let cool slightly before serving.