• Pre-heat the oven to 375°F.
• Spray baking sheet with non-stick spray.

To prepare the dough:

• In a medium bowl, combine masa flour, wheat flour and salt.
• Using a pastry blender, cut in butter until pea-size chunks are formed.
• Add egg and water, by the tablespoon, to the flour mixture until dough comes together to form a ball; rest for 10 minutes.
• Divide dough into 8 equal pieces; roll each piece into a 6-1/2-inch circle.

To prepare the filling:

• In a large skillet, over medium-high heat, cook the beef and onions, breaking up any lumps, until beef is evenly browned and no longer pink; drain.
• Add taco seasoning, tomatoes, green chilies, potato, garlic and water.
• Cook and stir 3 minutes or until most of water is absorbed; stir in cheese; season to taste with salt and pepper.

To prepare the empanadas:

• Divide the filling evenly, about 1/3 cup each, and place on the lower half of the dough circles, keeping it about 1/2-inch from edge.
• Fold dough in half; crimp edges with fork to seal or use an empanada press.
• Place empanadas on baking sheet and brush with corn oil.
• Prick tops with tines of fork to vent.
• Place in pre-heated oven and bake 30 minutes or until golden brown.